What OS? What version of Firefox? Did you try Firefox in Troubleshoot Mode? https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode#search104

See if one of the below help. https://support.mozilla.org/bm/questions/967316 https://support.mozilla.org/en-US/questions/1229392

Firefox package: firefox/jammy,now 124.0+build1-0ubuntu0.22.04.1~mt1 amd64 [installed] OS: kde neon Firefox was reinstalled and it did not fix the issue Opening it while holding shift nothing happens Edit: I also tried deleting files in /usr/local but nothing was there https://support.mozilla.org/en-US/questions/1143306 I also got the flatpak version working but I have none of my data

Firefox package: firefox/jammy,now 124.0+build1-0ubuntu0.22.04.1~mt1 amd64 [installed] OS: kde neon Firefox was reinstalled and it did not fix the issue Opening it while holding shiff does nothing Following this didn't help either https://support.mozilla.org/en-US/questions/1143306 I got the flatpak version working but I don't have any of my data

Did you ever use sync? Not sure, but maybe copying the data from your previous profile and moving it in the working profile folder may help. I think cor-el can better help with data to movement. https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data