Firefox stopped loading pages (including Preferences and about:config) and repeatedly prompts restart
Solution 1:
https://stackoverflow.com/questions/66337540/firefox-shows-only-blank-pages-even-aboutconfig-is-just-white
Turns out someone else also asked this question, and provided an answer as well. It is caused by the Citrix icaclient. Remove the current installed icaclient and reinstall it again without the app protection mode.
That's it.