Maybe these articles can help:

Safe Mode http://kb.mozillazine.org/Safe_Mode

Troubleshoot Firefox issues using Safe Mode https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode Take a look at the More information (Advanced users) at the end.

Also, Sync is not a backup service. It is a data transfer service and should probably be disconnected during troubleshooting.

RobertJ said

Maybe these articles can help: Safe Mode http://kb.mozillazine.org/Safe_Mode Troubleshoot Firefox issues using Safe Mode https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode Take a look at the More information (Advanced users) at the end. Also, Sync is not a backup service. It is a data transfer service and should probably be disconnected during troubleshooting.

After trying each additional configuration by disabling, deleting and whatnot, I can only think the problem has to do with the JIT compiler, as it's the only thing so far I couldn't find how to disable or modify in normal mozilla.--- And yes, "saving" isn't accurate I more likely referred to "sharing", as I only need to login once in the other device/profile, which I found funny was also kept in my old profile files.

What Firefox locale do you use and do you have language packs installed ?

• https://support.mozilla.org/en-US/kb/use-firefox-interface-other-languages-language-pack

Do a clean reinstall of the current Firefox release and delete the Firefox program folder before installing a fresh copy of the current Firefox release.

• download the Firefox installer and save the file to the desktop
  *https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

If possible uninstall your current Firefox version to cleanup the Windows Registry and settings in security software.

• do NOT remove "personal data" when you uninstall the current Firefox version, because this will remove all profile folders and you lose personal data like bookmarks and passwords including personal data in profiles created by other Firefox versions

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

• (64-bit Firefox) "C:\Program Files\Mozilla Firefox\"
• (32-bit Firefox) "C:\Program Files (x86)\Mozilla Firefox\"

• it is important to delete the Firefox program folder to remove all the files and make sure there are no problems with files that were leftover after uninstalling

Your personal data like bookmarks is stored in the Firefox profile folder, so you won't lose personal data when you reinstall or update Firefox, but make sure NOT to remove personal data when you uninstall Firefox as that will remove all Firefox profile folders and you lose your personal data.

• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data
• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Reinstall Firefox

• https://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems

cor-el said

What Firefox locale do you use and do you have language packs installed ?

• https://support.mozilla.org/en-US/kb/use-firefox-interface-other-languages-language-pack

---

Do a clean reinstall of the current Firefox release and delete the Firefox program folder before installing a fresh copy of the current Firefox release.

• download the Firefox installer and save the file to the desktop
  *https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

If possible uninstall your current Firefox version to cleanup the Windows Registry and settings in security software.

• do NOT remove "personal data" when you uninstall the current Firefox version, because this will remove all profile folders and you lose personal data like bookmarks and passwords including personal data in profiles created by other Firefox versions

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

• (64-bit Firefox) "C:\Program Files\Mozilla Firefox\"
• (32-bit Firefox) "C:\Program Files (x86)\Mozilla Firefox\"

• it is important to delete the Firefox program folder to remove all the files and make sure there are no problems with files that were leftover after uninstalling

Your personal data like bookmarks is stored in the Firefox profile folder, so you won't lose personal data when you reinstall or update Firefox, but make sure NOT to remove personal data when you uninstall Firefox as that will remove all Firefox profile folders and you lose your personal data.

---

• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data
• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Reinstall Firefox

• https://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems

Used default install that came with US English, no didn't have others. --- On Uninstall I didn't get the option to remove personal data, and it also removed automatically the program folders. I juggled a bit with uninstalling -> removing registry and cookies/cache -> reinstalling. This order kinda got it working with half profiles kept so I guess half a win:

1. Tried the linked firefox installer with locale UK English, 64 bits, same problem. Uninstall, cleanup registry and cache.
2. Same with 32 bits (british), no problem but most windows didn't load, most of my profile info lost. Same cleanup.
3. Re-tried to install 64 (british), no longer shows error. Kept most of my profile except for a few accounts disconnected but no biggies.

I also kept the safe-mode configuration (no hardware acceleration, default theme, no add-ons). Edit: I can now also return to normal configuration without trouble (hardware, add-ons)