diff --git a/__tests__/Date/wtf.unit.spec.js b/__tests__/Date/wtf.unit.spec.js
index 0d7625b..91ac5b9 100644
--- a/__tests__/Date/wtf.unit.spec.js
+++ b/__tests__/Date/wtf.unit.spec.js
@@ -1,18 +1,23 @@
+/**
+ * @jest-environment jsdom
+ */
+
 // SRC: https://jsdate.wtf/
 describe('Date', () => {
   'use strict'
 
-  let oDate, dateString, dateValue, milliseconds
+  let oDate, dateISOString, dateTimeString, dateValue, milliseconds
 
   // 1 of 28
   describe('new Date("0")', () => {
     beforeEach(() => {
       oDate = new Date('0')
-      dateString = oDate.toISOString()
+      dateISOString = oDate.toISOString()
+      dateTimeString = oDate.toTimeString()
     })
 
     it('does NOT equal "1970-01-01T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('1970-01-01T00:00:00.000Z')
+      expect(dateISOString).not.toEqual('1970-01-01T00:00:00.000Z')
     })
 
     it('interprets "0" as the year 2000, not as a timestamp! parsing it as "2000-01-01T06:00:00.000"', () => {
@@ -27,17 +32,17 @@ describe('Date', () => {
   describe('new Date(0)', () => {
     beforeEach(() => {
       oDate = new Date(0)
-      dateString = oDate.toISOString()
+      dateISOString = oDate.toISOString()
     })
 
     it('does NOT equal "2000-01-01T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2000-01-01T00:00:00.000Z')
+      expect(dateISOString).not.toEqual('2000-01-01T00:00:00.000Z')
     })
 
     it('is interpreted as 0 milliseconds since the Unix epoch (Jan 1, 1970).', () => {
       // The number 0, as opposed to the string "0",
       // is interpreted as milliseconds since the Unix epoch (Jan 1, 1970).
-      expect(dateString).toEqual('1970-01-01T00:00:00.000Z')
+      expect(dateISOString).toEqual('1970-01-01T00:00:00.000Z')
     })
   })
 
@@ -116,20 +121,20 @@ describe('Date', () => {
     // 7 of 28
     describe('.toTimeString()', () => {
       beforeEach(() => {
-        dateString = oDate.toTimeString()
+        dateTimeString = oDate.toTimeString()
       })
 
       it('does NOT equal ""', () => {
-        expect(dateString).not.toEqual('')
+        expect(dateTimeString).not.toEqual('')
       })
 
       it('is NOT null', () => {
-        expect(dateString).not.toBe(null)
+        expect(dateTimeString).not.toBe(null)
       })
 
       it('returns the string "Invalid Date" for invalid dates. 🫠', () => {
         // toTimeString() returns the string "Invalid Date" for invalid dates. 🫠
-        expect(dateString).toEqual('Invalid Date')
+        expect(dateTimeString).toEqual('Invalid Date')
       })
     })
   })
@@ -138,15 +143,15 @@ describe('Date', () => {
   describe('new Date("1")', () => {
     beforeEach(() => {
       oDate = new Date('1')
-      dateString = oDate.toISOString()
+      dateISOString = oDate.toISOString()
     })
 
     it('does NOT equal "1970-01-01T00:00:00.001Z"', () => {
-      expect(dateString).not.toEqual('1970-01-01T00:00:00.001Z')
+      expect(dateISOString).not.toEqual('1970-01-01T00:00:00.001Z')
     })
 
     it('does NOT equal "0001-01-01T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('0001-01-01T00:00:00.000Z')
+      expect(dateISOString).not.toEqual('0001-01-01T00:00:00.000Z')
     })
 
     it('equals to "2001-01-01T00:00:00.000"', () => {
@@ -162,15 +167,15 @@ describe('Date', () => {
   describe('new Date("2")', () => {
     beforeEach(() => {
       oDate = new Date('2')
-      dateString = oDate.toISOString()
+      dateISOString = oDate.toISOString()
     })
 
     it('does NOT equal "2002-01-01T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2002-01-01T00:00:00.000Z')
+      expect(dateISOString).not.toEqual('2002-01-01T00:00:00.000Z')
     })
 
     it('does NOT equal "2001-01-02T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2001-01-02T00:00:00.000Z')
+      expect(dateISOString).not.toEqual('2001-01-02T00:00:00.000Z')
     })
 
     it('equals "2001-02-01T00:00:00.000"', () => {
@@ -184,15 +189,15 @@ describe('Date', () => {
   describe('new Date("12")', () => {
     beforeEach(() => {
       oDate = new Date('12')
-      dateString = oDate.toISOString()
+      dateISOString = oDate.toISOString()
     })
 
     it('does NOT equal "2012-01-01T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2012-01-01T00:00:00.000Z')
+      expect(dateISOString).not.toEqual('2012-01-01T00:00:00.000Z')
     })
 
     it('does NOT equal "2001-01-12T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2001-01-12T00:00:00.000Z')
+      expect(dateISOString).not.toEqual('2001-01-12T00:00:00.000Z')
     })
 
     it('equals "2001-12-01T00:00:00.000"', () => {
@@ -207,7 +212,7 @@ describe('Date', () => {
   describe('new Date("13")', () => {
     beforeEach(() => {
       oDate = new Date('13')
-      dateString = oDate.toTimeString()
+      dateTimeString = oDate.toTimeString()
     })
 
     describe('.toISOString()', () => {
@@ -219,7 +224,7 @@ describe('Date', () => {
     describe('.toTimeString()', () => {
       it('equals "Invalid Date"', () => {
         // "13" would be month 13, which doesn't exist, so it's Invalid Date.
-        expect(dateString).toEqual('Invalid Date')
+        expect(dateTimeString).toEqual('Invalid Date')
       })
     })
   })
@@ -255,36 +260,58 @@ describe('Date', () => {
   describe('new Date("12.1")', () => {
     beforeEach(() => {
       oDate = new Date('12.1')
-      dateString = oDate.toISOString()
-    })
-
-    it('does NOT equal "2001-01-01T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2001-01-01T00:00:00.000Z')
     })
 
-    it('does NOT equal "2012-01-01T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2012-01-01T00:00:00.000Z')
-    })
+    if (isFireFox()) { // v 143.0
+      describe('@FireFox', () => {
+        describe('.toISOString()', () => {
+          it('throws', () => {
+            expect(() => oDate.toISOString()).toThrow()
+          })
+        })
 
-    it('equals "2001-12-01T00:00:00.000"', () => {
-      // "12.1" is interpreted as the date December 1st,
-      // and as before for dates with no year the default is 2001 because of course.
-      // expect(dateString).toEqual('2001-12-01T00:00:00.000Z')
-      const expectedDate = new Date('2001-12-01T00:00:00.000')
-      expect(oDate.getTime()).toEqual(expectedDate.getTime())
-    })
+        describe('.toTimeString()', () => {
+          it('equals "Invalid Date"', () => {
+            expect(dateTimeString).toEqual('Invalid Date')
+          })
+        })
+      })
+    } else {
+      describe('.toISOString()', () => {
+        beforeEach(() => {
+          // NOTE: FireFox throws here: "Invalid Date".
+          dateISOString = oDate.toISOString()
+        })
+
+        it('does NOT equal "2001-01-01T00:00:00.000Z"', () => {
+          expect(dateISOString).not.toEqual('2001-01-01T00:00:00.000Z')
+        })
+
+        it('does NOT equal "2012-01-01T00:00:00.000Z"', () => {
+          expect(dateISOString).not.toEqual('2012-01-01T00:00:00.000Z')
+        })
+
+        it('equals "2001-12-01T00:00:00.000"', () => {
+          // "12.1" is interpreted as the date December 1st,
+          // and as before for dates with no year the default is 2001 because of course.
+          // expect(dateString).toEqual('2001-12-01T00:00:00.000Z')
+          const expectedDate = new Date('2001-12-01T00:00:00.000')
+          expect(oDate.getTime()).toEqual(expectedDate.getTime())
+        })
+      })
+    }
   })
 
   // 15 of 28
   describe('new Date("12.0")', () => {
     beforeEach(() => {
       oDate = new Date('12.0')
-      dateString = oDate.toTimeString()
+      dateTimeString = oDate.toTimeString()
     })
 
     describe('.toTimeString()', () => {
       it('equals "Invalid Date"', () => {
-        expect(dateString).toEqual('Invalid Date')
+        expect(dateTimeString).toEqual('Invalid Date')
       })
     })
 
@@ -299,34 +326,56 @@ describe('Date', () => {
   describe('new Date("12.-1")', () => {
     beforeEach(() => {
       oDate = new Date('12.-1')
-      dateString = oDate.toISOString()
     })
 
-    it('does NOT equal "2012-01-01T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2012-01-01T00:00:00.000Z')
-    })
-
-    it('does NOT equal "2001-01-01T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2001-01-01T00:00:00.000Z')
-    })
+    if (isFireFox()) { // v 143.0
+      describe('@FireFox', () => {
+        describe('.toISOString()', () => {
+          it('throws', () => {
+            expect(() => oDate.toISOString()).toThrow()
+          })
+        })
 
-    it('ignores the "-", interpreting it like "12.1", resulting in "2001-12-01T00:00:00.000"', () => {
-      // The dash here is ignored, so this is interpreted the same as "12.1".
-      // expect(dateString).toEqual('2001-12-01T00:00:00.000Z')
-      const expectedDate = new Date('2001-12-01T00:00:00.000')
-      expect(oDate.getTime()).toEqual(expectedDate.getTime())
-    })
+        describe('.toTimeString()', () => {
+          it('equals "Invalid Date"', () => {
+            expect(dateTimeString).toEqual('Invalid Date')
+          })
+        })
+      })
+    } else {
+      describe('.toISOString()', () => {
+        beforeEach(() => {
+          // NOTE: FireFox throws here "Invalid Date".
+          dateISOString = oDate.toISOString()
+        })
+
+        it('does NOT equal "2012-01-01T00:00:00.000Z"', () => {
+          expect(dateISOString).not.toEqual('2012-01-01T00:00:00.000Z')
+        })
+
+        it('does NOT equal "2001-01-01T00:00:00.000Z"', () => {
+          expect(dateISOString).not.toEqual('2001-01-01T00:00:00.000Z')
+        })
+
+        it('ignores the "-", interpreting it like "12.1", resulting in "2001-12-01T00:00:00.000"', () => {
+          // The dash here is ignored, so this is interpreted the same as "12.1".
+          // expect(dateString).toEqual('2001-12-01T00:00:00.000Z')
+          const expectedDate = new Date('2001-12-01T00:00:00.000')
+          expect(oDate.getTime()).toEqual(expectedDate.getTime())
+        })
+      })
+    }
   })
 
   // 17 of 28
   describe('new Date("perhaps 1")', () => {
     beforeEach(() => {
       oDate = new Date('perhaps 1')
-      dateString = oDate.toISOString()
+      dateISOString = oDate.toISOString()
     })
 
     it('does NOT equal "1970-01-01T00:00:01.000Z"', () => {
-      expect(dateString).not.toEqual('1970-01-01T00:00:01.000Z')
+      expect(dateISOString).not.toEqual('1970-01-01T00:00:01.000Z')
     })
 
     it('ignores leading text. Finding "1" and parsing it as January. Resulting in "2001-01-01T00:00:00.000"', () => {
@@ -345,12 +394,12 @@ describe('Date', () => {
       // It needs a number to parse, so this is Invalid Date.
       // It's equivalent to new Date("").
       oDate = new Date('perhaps')
-      dateString = oDate.toTimeString()
+      dateTimeString = oDate.toTimeString()
     })
 
     describe('.toTimeString()', () => {
       it('equals "Invalid Date"', () => {
-        expect(dateString).toEqual('Invalid Date')
+        expect(dateTimeString).toEqual('Invalid Date')
       })
     })
 
@@ -368,23 +417,45 @@ describe('Date', () => {
       // And for some reason this expression cares about your local timezone,
       // which happens to be BST for me right now.
       oDate = new Date('maybe 1')
-      dateString = oDate.toISOString()
     })
 
-    // WARNING: The quiz says this is the correct answer!
-    it('does NOT equal "2001-04-30T23:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2001-04-30T23:00:00.000Z')
-    })
+    if (isFireFox()) { // v 143.0
+      describe('@FireFox', () => {
+        describe('.toISOString()', () => {
+          it('throws', () => {
+            expect(() => oDate.toISOString()).toThrow()
+          })
+        })
 
-    it('does NOT equal "2001-01-01T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2001-01-01T00:00:00.000Z')
-    })
-
-    it('parses "maybe" as "may"! resulting in "2001-05-01T00:00:00.000"', () => {
-      // expect(dateString).toEqual('2001-05-01T00:00:00.000Z')
-      const expectedDate = new Date('2001-05-01T00:00:00.000')
-      expect(oDate.getTime()).toEqual(expectedDate.getTime())
-    })
+        describe('.toTimeString()', () => {
+          it('equals "Invalid Date"', () => {
+            expect(dateTimeString).toEqual('Invalid Date')
+          })
+        })
+      })
+    } else {
+      describe('.toISOString()', () => {
+        beforeEach(() => {
+          // NOTE: FireFox throws here: "Invalid Date".
+          dateISOString = oDate.toISOString()
+        })
+
+        // WARNING: The quiz says this is the correct answer!
+        it('does NOT equal "2001-04-30T23:00:00.000Z"', () => {
+          expect(dateISOString).not.toEqual('2001-04-30T23:00:00.000Z')
+        })
+
+        it('does NOT equal "2001-01-01T00:00:00.000Z"', () => {
+          expect(dateISOString).not.toEqual('2001-01-01T00:00:00.000Z')
+        })
+
+        it('parses "maybe" as "may"! resulting in "2001-05-01T00:00:00.000"', () => {
+          // expect(dateString).toEqual('2001-05-01T00:00:00.000Z')
+          const expectedDate = new Date('2001-05-01T00:00:00.000')
+          expect(oDate.getTime()).toEqual(expectedDate.getTime())
+        })
+      })
+    }
   })
 
   // 20 of 28
@@ -394,23 +465,46 @@ describe('Date', () => {
       // this is just parsing "may 2010"
       // and again local timezone is important.
       oDate = new Date('fourth of may 2010')
-      dateString = oDate.toISOString()
     })
 
-    // Works only in non-UTC timezones.
-    xit('does NOT equal "2010-05-01T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2010-05-01T00:00:00.000Z')
-    })
+    if (isFireFox()) { // v 143.0
+      describe('@FireFox', () => {
+        describe('.toISOString()', () => {
+          it('throws', () => {
+            expect(() => oDate.toISOString()).toThrow()
+          })
+        })
 
-    it('does NOT equal "2010-05-04T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2010-05-04T00:00:00.000Z')
-    })
-
-    it('ignores "fourth of", parsing "may 2010" as "2010-05-01T00:00:00.000"', () => {
-      // expect(dateString).toEqual('2010-05-01T00:00:00.000Z')
-      const expectedDate = new Date('2010-05-01T00:00:00.000')
-      expect(oDate.getTime()).toEqual(expectedDate.getTime())
-    })
+        describe('.toTimeString()', () => {
+          it('equals "Invalid Date"', () => {
+            expect(dateTimeString).toEqual('Invalid Date')
+          })
+        })
+      })
+    } else {
+      describe('.toISOString()', () => {
+        beforeEach(() => {
+          // NOTE: FireFox throws here: "Invalid Date".
+          dateISOString = oDate.toISOString()
+        })
+
+        // Only works in Non-UTC
+        xit('does NOT equal "2010-05-01T00:00:00.000"', () => {
+          const expectedDate = new Date('2010-05-01T00:00:00.000')
+          expect(oDate.getTime()).not.toEqual(expectedDate.getTime())
+        })
+
+        it('does NOT equal "2010-05-04T00:00:00.000Z"', () => {
+          expect(dateISOString).not.toEqual('2010-05-04T00:00:00.000Z')
+        })
+
+        it('ignores "fourth of", parsing "may 2010" as "2010-05-01T00:00:00.000"', () => {
+          // expect(dateString).toEqual('2010-05-01T00:00:00.000Z')
+          const expectedDate = new Date('2010-05-01T00:00:00.000')
+          expect(oDate.getTime()).toEqual(expectedDate.getTime())
+        })
+      })
+    }
   })
 
   // 21 of 28
@@ -418,20 +512,42 @@ describe('Date', () => {
     beforeEach(() => {
       // UTC is correctly parsed as a timezone.
       oDate = new Date('May 4 UTC')
-      dateString = oDate.toISOString()
-    })
-
-    it('does NOT equal "2010-04-30T23:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2010-04-30T23:00:00.000Z')
     })
 
-    it('does NOT equal "2010-05-01T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2010-05-01T00:00:00.000Z')
-    })
+    if (isFireFox()) { // v 143.0
+      describe('@FireFox', () => {
+        describe('.toISOString()', () => {
+          it('throws', () => {
+            expect(() => oDate.toISOString()).toThrow()
+          })
+        })
 
-    it('parses UTC as "2001-05-04T00:00:00.000Z"', () => {
-      expect(dateString).toEqual('2001-05-04T00:00:00.000Z')
-    })
+        describe('.toTimeString()', () => {
+          it('equals "Invalid Date"', () => {
+            expect(dateTimeString).toEqual('Invalid Date')
+          })
+        })
+      })
+    } else {
+      describe('.toISOString()', () => {
+        beforeEach(() => {
+          // NOTE: FireFox throws here: "Invalid Date".
+          dateISOString = oDate.toISOString()
+        })
+
+        it('does NOT equal "2010-04-30T23:00:00.000Z"', () => {
+          expect(dateISOString).not.toEqual('2010-04-30T23:00:00.000Z')
+        })
+
+        it('does NOT equal "2010-05-01T00:00:00.000Z"', () => {
+          expect(dateISOString).not.toEqual('2010-05-01T00:00:00.000Z')
+        })
+
+        it('parses UTC as "2001-05-04T00:00:00.000Z"', () => {
+          expect(dateISOString).toEqual('2001-05-04T00:00:00.000Z')
+        })
+      })
+    }
   })
 
   // 22 of 28
@@ -439,21 +555,43 @@ describe('Date', () => {
     beforeEach(() => {
       // You can add modifiers to timezones and it works as you would expect.
       oDate = new Date('May 4 UTC+1')
-      dateString = oDate.toISOString()
     })
 
-    it('does NOT equal "2001-05-04T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2001-05-04T00:00:00.000Z')
-    })
+    if (isFireFox()) { // v 143.0
+      describe('@FireFox', () => {
+        describe('.toISOString()', () => {
+          it('throws', () => {
+            expect(() => oDate.toISOString()).toThrow()
+          })
+        })
 
-    it('does NOT equal "2010-05-01T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2010-05-01T00:00:00.000Z')
-    })
-
-    it('parses UTC+1 as "2001-05-04T00:00:00.000", resulting in "2001-05-03T23:00:00.000Z"', () => {
-      // 05-04T00 @ UTC+1 is 1 hr ahead: 05-03T23 @ UTC
-      expect(dateString).toEqual('2001-05-03T23:00:00.000Z')
-    })
+        describe('.toTimeString()', () => {
+          it('equals "Invalid Date"', () => {
+            expect(dateTimeString).toEqual('Invalid Date')
+          })
+        })
+      })
+    } else {
+      describe('.toISOString()', () => {
+        beforeEach(() => {
+          // NOTE: FireFox throws here: "Invalid Date".
+          dateISOString = oDate.toISOString()
+        })
+
+        it('does NOT equal "2001-05-04T00:00:00.000Z"', () => {
+          expect(dateISOString).not.toEqual('2001-05-04T00:00:00.000Z')
+        })
+
+        it('does NOT equal "2010-05-01T00:00:00.000Z"', () => {
+          expect(dateISOString).not.toEqual('2010-05-01T00:00:00.000Z')
+        })
+
+        it('parses UTC+1 as "2001-05-04T00:00:00.000", resulting in "2001-05-03T23:00:00.000Z"', () => {
+          // 05-04T00 @ UTC+1 is 1 hr ahead: 05-03T23 @ UTC
+          expect(dateISOString).toEqual('2001-05-03T23:00:00.000Z')
+        })
+      })
+    }
   })
 
   // 23 of 28
@@ -461,16 +599,38 @@ describe('Date', () => {
     beforeEach(() => {
       // It also supports minutes!
       oDate = new Date('May 4 UTC+1:59')
-      dateString = oDate.toISOString()
     })
 
-    it('does NOT equal "2001-05-04T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2001-05-04T00:00:00.000Z')
-    })
+    if (isFireFox()) { // v 143.0
+      describe('@FireFox', () => {
+        describe('.toISOString()', () => {
+          it('throws', () => {
+            expect(() => oDate.toISOString()).toThrow()
+          })
+        })
 
-    it('parses UTC+1:59 as "2001-05-04T00:00:00.000", resulting in "2001-05-03T22:01:00.000Z"', () => {
-      expect(dateString).toEqual('2001-05-03T22:01:00.000Z')
-    })
+        describe('.toTimeString()', () => {
+          it('equals "Invalid Date"', () => {
+            expect(dateTimeString).toEqual('Invalid Date')
+          })
+        })
+      })
+    } else {
+      describe('.toISOString()', () => {
+        beforeEach(() => {
+          // NOTE: FireFox throws here: "Invalid Date".
+          dateISOString = oDate.toISOString()
+        })
+
+        it('does NOT equal "2001-05-04T00:00:00.000Z"', () => {
+          expect(dateISOString).not.toEqual('2001-05-04T00:00:00.000Z')
+        })
+
+        it('parses UTC+1:59 as "2001-05-04T00:00:00.000", resulting in "2001-05-03T22:01:00.000Z"', () => {
+          expect(dateISOString).toEqual('2001-05-03T22:01:00.000Z')
+        })
+      })
+    }
   })
 
   // 24 of 28
@@ -480,19 +640,25 @@ describe('Date', () => {
       // 60 is being parsed as the year here,
       // UTC+1 is the timezone.
       oDate = new Date('May 4 UTC+1:60')
-      dateString = oDate.toISOString()
     })
 
-    it('does NOT equal "2001-05-04T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2001-05-04T00:00:00.000Z')
-    })
+    describe('.toISOString()', () => {
+      beforeEach(() => {
+        // NOTE: FireFox throws here: "Invalid Date".
+        dateISOString = oDate.toISOString()
+      })
 
-    it('does NOT equal "2001-05-03T22:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2001-05-03T22:00:00.000Z')
-    })
+      it('does NOT equal "2001-05-04T00:00:00.000Z"', () => {
+        expect(dateISOString).not.toEqual('2001-05-04T00:00:00.000Z')
+      })
 
-    it('parses UTC+1:60 as "UTC+1" AND "year 60"!, resulting in "1960-05-03T23:00:00.000Z"', () => {
-      expect(dateString).toEqual('1960-05-03T23:00:00.000Z')
+      it('does NOT equal "2001-05-03T22:00:00.000Z"', () => {
+        expect(dateISOString).not.toEqual('2001-05-03T22:00:00.000Z')
+      })
+
+      it('parses UTC+1:60 as "UTC+1" AND "year 60"!, resulting in "1960-05-03T23:00:00.000Z"', () => {
+        expect(dateISOString).toEqual('1960-05-03T23:00:00.000Z')
+      })
     })
   })
 
@@ -501,12 +667,12 @@ describe('Date', () => {
     beforeEach(() => {
       // No tricks here, just a plain ol' Invalid Date.
       oDate = new Date('1990 2010')
-      dateString = oDate.toTimeString()
+      dateTimeString = oDate.toTimeString()
     })
 
     describe('.toTimeString()', () => {
       it('equals "Invalid Date"', () => {
-        expect(dateString).toEqual('Invalid Date')
+        expect(dateTimeString).toEqual('Invalid Date')
       })
     })
 
@@ -522,15 +688,15 @@ describe('Date', () => {
     beforeEach(() => {
       // For some reason, parenthesised text is ignored.
       oDate = new Date('1990 (2010)')
-      dateString = oDate.toISOString()
+      dateISOString = oDate.toISOString()
     })
 
     it('does NOT equal "2000-01-01T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2000-01-01T00:00:00.000Z')
+      expect(dateISOString).not.toEqual('2000-01-01T00:00:00.000Z')
     })
 
     it('does NOT equal "2010-01-01T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2010-01-01T00:00:00.000Z')
+      expect(dateISOString).not.toEqual('2010-01-01T00:00:00.000Z')
     })
 
     it('ignores text in parentheses, parsing this as "1990", resulting in "1990-01-01T00:00:00.000"', () => {
@@ -545,15 +711,15 @@ describe('Date', () => {
     beforeEach(() => {
       // No matter where it is.
       oDate = new Date('(1990) 2010')
-      dateString = oDate.toISOString()
+      dateISOString = oDate.toISOString()
     })
 
     it('does NOT equal "1990-01-01T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('1990-01-01T00:00:00.000Z')
+      expect(dateISOString).not.toEqual('1990-01-01T00:00:00.000Z')
     })
 
     it('does NOT equal "2000-01-01T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2000-01-01T00:00:00.000Z')
+      expect(dateISOString).not.toEqual('2000-01-01T00:00:00.000Z')
     })
 
     it('ignores text in parentheses, parsing this as "2010", resulting in "2010-01-01T00:00:00.000"', () => {
@@ -569,15 +735,15 @@ describe('Date', () => {
       // -[] is coerced to 0,
       // which is interpreted as milliseconds since the Unix epoch (Jan 1, 1970).
       oDate = new Date(-[])
-      dateString = oDate.toISOString()
+      dateISOString = oDate.toISOString()
     })
 
     it('does NOT equal "2000-01-01T00:00:00.000Z"', () => {
-      expect(dateString).not.toEqual('2000-01-01T00:00:00.000Z')
+      expect(dateISOString).not.toEqual('2000-01-01T00:00:00.000Z')
     })
 
     it('coerces -[] as 0, parsing it to "1970-01-01T00:00:00.000Z"', () => {
-      expect(dateString).toEqual('1970-01-01T00:00:00.000Z')
+      expect(dateISOString).toEqual('1970-01-01T00:00:00.000Z')
     })
   })
 })
diff --git a/__tests__/global.js b/__tests__/global.js
index 8b71eda..48b6bd2 100644
--- a/__tests__/global.js
+++ b/__tests__/global.js
@@ -1 +1,16 @@
+function isFireFox () {
+  if (!navigator) {
+    return false
+  }
+
+  const userAgent = navigator
+    .userAgent
+    .toLowerCase()
+
+  return userAgent.indexOf('firefox') > -1
+}
+
 global._ = require('lodash')
+
+// A simple function to detect Firefox from the user agent
+global.isFireFox = isFireFox
diff --git a/package.json b/package.json
index 77759e6..c0ada70 100644
--- a/package.json
+++ b/package.json
@@ -26,7 +26,9 @@
       "jest"
     ],
     "globals": [
-      "_"
+      "navigator",
+      "_",
+      "isFireFox"
     ]
   },
   "repository": {