That actually seems to help for me.
I disabled hardware acceleration in Firefox and made sure I closed my soundcards mixer (which also has some direct2d acceleration) and I haven't had FF crash so far.
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Check your GPU temps when the crash happens...
When i had my old (dying) GPU FFXIV crashed constantly whenever there was a little bit more stuff to do, and the "best" fix for me at that point for whatever reason was to limit FPS to 30.
i've crashed 19 times today, i've done all of the steps listed and submitted several emails for help and gotten 0 responses, i'm not sure my problem is 100% the same i'm still getting the same direct x error but it only happens when i'm using my 2080ti and my 144hz refresh rate display. please advise