Version: cimg/node:25.4.0-browsers
The environment parameter INSTALL_XFVB doesn't match the name of the service Xvfb. The letters F and V are transposed and this is likely to cause confusion and mistakes when attempting to use the parameter.
Xvfb stands for X virtual frame buffer https://en.wikipedia.org/wiki/Xvfb
Suggestion
Change INSTALL_XFVB to INSTALL_XVFB in script and documentation