Maybe Fission related. (DOMFissionEnabled=1)

Crash report: https://crash-stats.mozilla.org/report/index/67bc96ad-aae1-4458-8fdb-965580220313

MOZ_CRASH Reason: MOZ_DIAGNOSTIC_ASSERT(wl_container->surface) (Should have surface if we're ready to draw)

Top 10 frames of crashing thread:

0 libxul.so libxul.so@0x0000000003569103 
1 libxul.so libxul.so@0x000000000356913a 
2 libxul.so libxul.so@0x0000000000c642d5 
3 libxul.so libxul.so@0x0000000000c4dfa7 
4 libxul.so libxul.so@0x0000000000c4d318 
5 libxul.so libxul.so@0x0000000000c4d50e 
6 libxul.so libxul.so@0x0000000000c65d51 
7 libxul.so libxul.so@0x0000000000c5988c 
8 libxul.so libxul.so@0x0000000000c5ddd7 
9 libxul.so libxul.so@0x00000000012bd4d7 

I am on Ubuntu 21.10 using Firefox Beta via Snap. https://snapcraft.io/firefox

The severity field is not set for this bug.
:bhood, could you have a look please?

For more information, please visit auto_nag documentation.

The bug has a crash signature, thus the bug will be considered confirmed.

Glenn, could you please evaluate the severity on this when you get a chance? Let's be sure it's not more severe than S3.

I am also available to answer questions or investigate things. I am reasonably technical (as a web developer mostly). This crash I believe has only happened once for me though.

I can't actually find this assert anywhere in the current m-c codebase? Perhaps stransky knows if this assert has been removed?

Yes that was removed by Bug 1761870.