Windows 10 reached EOS (end of support) on October 14, 2025. If you are on Windows 10, see this article.

Search Support

Avoid support scams. We will never ask you to call or text a phone number or share personal information. Please report suspicious activity using the “Report Abuse” option.

Learn More
Echekwara

Why does Firefox always start up windowed instead of in fullscreen?

ottomotor

My installation of Firefox always starts up in windowed mode, even though I only ever use it in fullscreen. I thought that it might have been that I enabled privacy.resistFingerprinting, but that wasn't it. I also tried refreshing and then reinstalling Firefox, and that didn't work either. Could it maybe be some other setting that I might not even remember having changed? Or is my Sync account just broken?

My installation of Firefox always starts up in windowed mode, even though I only ever use it in fullscreen. I thought that it might have been that I enabled privacy.resistFingerprinting, but that wasn't it. I also tried refreshing and then reinstalling Firefox, and that didn't work either. Could it maybe be some other setting that I might not even remember having changed? Or is my Sync account just broken?

All Replies (8)

https://support.mozilla.org/en-US/kb/changes-toolbars-and-window-sizes-are-not-saved You may have corrupt xulstore.json file.

Close Firefox. Open your file browser to this hidden location:

  • Mac: *~/Library/Application Support/Firefox/Profiles
  • Linux: *~/.mozilla/firefox/Profiles
  • Windows: %AppData%\Mozilla\Firefox\Profiles
  • *C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles
  • Windows XP: C:\Documents and Settings\<user>\Application Data
    \Mozilla\Firefox\Profiles\

Search for the above files. Then rename or delete them. Restart Firefox.

Alright, that worked, thanks! Because of how that article was phrased, I thought that refreshing Firefox also created a new profile, but apparently not. Should have read it more closely I guess :D

Glad to help. Safe Surfing.

Okay, just now I started Firefox and it opened up windowed again, and this time, deleting xulstore.json doesn't work. Do I have to refresh Firefox now? And do you know how xulstore.json becomes corrupted?

https://support.mozilla.org/en-US/kb/update-firefox-latest-version?cache=no Did you update Firefox to the latest version 66.0.4 May 5, 2019 Fixes add-on certificate issue.

Yes, I just checked and then deleted the file again (in case the update had just happened) and the issue is still there :|

Well, after resetting / deleting / whatever my profile, reinstalling Firefox etc, I figured that my Firefox Sync account might have had something to do with it, since it always works for a while after I do one of the above, and at some point it randomly starts going windowed again. I have now done a reinstall without syncing with my previous Sync account, and so far it's worked. Let's see if it stays that way.