You can check if you have a user.js file in the profile folder to initialize prefs each time Firefox starts. The user.js file will only be present if you or other software has created this file and normally won't be present.

You can check its content with a text editor (right-click: "Open with"; do not double-click). The user.js file is read each time Firefox is started and initializes preferences to the value specified in this file, so preferences set via user.js can only be changed temporarily for the current session.

You can delete the user.js file if you didn't create this file yourself.

• https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory/Folder:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/Profiles

Oh does the user.js file override the prefs.js file? I neglected it since it said it was modified less recently than the prefs.js file but I guess since its read not written to it would stay the same date.

That's probably the reason, I'll have to check when I get home.

A bit strange that changing restore session on startup wasn't reverting since I turned that back on for convenience, possibly it happens before user.js is read for the current session.

Thanks

The user.js file is always read each time you start Firefox. You can modify prefs for the current session via about:config, but these changes are lost when you close and restart Firefox and the pref values as set via user.js are applied. That is how user.js works, it is useful to set prefs that you frequently modify to a known default state or you can use user.js to initialize a profile and rename the file once this has been done.

cor-el said

The user.js file is always read each time you start Firefox. You can modify prefs for the current session via about:config, but these changes are lost when you close and restart Firefox and the pref values as set via user.js are applied. That is how user.js works, it is useful to set prefs that you frequently modify to a known default state or you can use user.js to initialize a profile and rename the file once this has been done.

Thanks this really clears up my confusion between the 2 different .js files. I moved the user.js file to a different folder and it solve the problem. Thanks for the help!