[zamadatix]

I don't use Firefox currently but I did for a couple years recently. For a while Teams was blocked and/or broken in Firefox due to calling features Firefox didn't have at the time.

A few sites would silently break, e.g. restaurant online order pages, but work in Chrome. Never really looked into why, it was just annoying and intermittent (might work one month but not the next).

YouTube occasionally had some issues. For a while it was on an old version of Polymer that used Shadow DOM V0 (experimental) instead of V1.

A good list is here https://webcompat.com/issues?page=1&per_page=100&state=open&... keep in mind some of these are "is extremely slow in Firefox". Sometimes that's just that Firefox didn't have the same set of optimizations (not necessarily even fewer optimizations, just not ones built against) and other times that's deeper seated like the Shaw DOM V0 example where the fallback for the page was to use some older.