For me, a fatal flaw with Firefox is that canvas getImageData doesn’t work like any other browser. Instead of returning the pixel values for the image loaded into the canvas, it gives the pixel values after they’ve been modified by the current screen/OS color profile. Other browsers seem to maintain the actual pixel values even if the OS later modifies the visual output of the application.

This means that any user trying to do any data work with my GIS software will regularly get wrong outputs if they use Firefox.