Looks font-related, possibly a bad font. Does it still happen in Troubleshoot Mode?

Try changing gfx.e10s.font-list.shared and/or gfx.font-list-omt.enabled to false in about:config then restart the browser.

There are no symbols for your libfontconfig.so on the Socorro server, so it not possible to check out the report.

Does this happen when you visit specific pages ? What font do you use as the default font for Firefox (UI and webpages)?

Does it make a difference whether for Enhanced Tracking Protection Known fingerprinters and Suspected fingerprinters are enabled or disabled.

@cor-el - It does happen when opening any web page. - Default font is Noto Serif - It was enabled, I will disable both features and check.

Thanks cor-el

@zeroknight - It did happen in normal and Troubleshoot mode. - I will check changing the font though as you suggested

Thanks zeroknight

If it still happens in Troubleshoot Mode then don't bother changing those settings.

Does it still happen with the flatpak package?