unexpectedly not compatible with SeaMonkey 2.49.1

[grahamperrin]

https://addons.mozilla.org/seamonkey/addon/its-all-text/versions/1.9.3

Works with Firefox 45.0 - 56.*, SeaMonkey 2.12 - 2.50.*

When I attempt to install the extension, it is reportedly:

… not compatible with SeaMonkey 2.49.1.

Environment

User agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:52.0) Gecko/20100101 Firefox/52.0 SeaMonkey/2.49.1

Build identifier: 20171112111759

[docwhat]

Huh. Dunno... I haven't been managing the SeaMonkey stuff... IAT is pretty much dead now due to Firefox 57.