STR: * add in a Web Extensions add-on into about:addons, for example https://github.com/bwinton/catgif-extension * go to about:support * Firefox crashes AbortMessage:  ###!!! ABORT: Invalid backend: file /builds/slave/m-cen-m64-ntly-000000000000000/build/src/gfx/layers/client/ClientLayerManager.cpp, line 776
Can you look in about:crashes for a crash stack?
(In reply to Bill McCloskey (:billm) from comment #1) > Can you look in about:crashes for a crash stack? https://crash-stats.mozilla.com/report/index/d6f358dd-f2ac-4775-91ea-5f73b2151023
It looks like this is happening here: https://dxr.mozilla.org/mozilla-central/source/toolkit/modules/Troubleshoot.jsm#315 when the loop gets to one of our background windows.
Duping to 1218364 since Luca already has a patch in the works.