See:

• http://kb.mozillazine.org/Preferences_not_saved

This issue can also be caused by an extension that isn't working properly.

In Firefox 4 you can use one of these to start in Safe mode:

• Help > Restart with Add-ons Disabled
• Hold down the Shift key while double clicking the Firefox desktop shortcut (Windows)

If it does work in Safe mode then disable all extensions and then try to find which is causing it by enabling one at a time until the problem reappears.

• Use "Disable all add-ons" on the Safe mode start window to disable all extensions.
• Close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")

See also:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

I have been having this problem for MONTHS! since leaving version 3.6. No one on the support desks have been able to tell me why v3 holds and then it goes funky when updated.

I have deleted FF --- and even installed on a different drive --- and the problem persists. The upgrade to newer versions, for me, is greatly diminished by this chronically persistent connection problem.

Fire fox I am greatly disappointed that you keep releasing new versions without correcting this problem.

cor-el, your solution: " This issue can also be caused by an extension that isn't working properly.

In Firefox 4 you can use one of these to start in Safe Mode:

   Help > Restart with Add-ons Disabled

   Hold down the Shift key while double clicking the Firefox desktop shortcut (Windows) '

If it does work in Safe Mode then disable all extensions and then try to find which is causing it by enabling one at a time until the problem reappears.

   Use "Disable all add-ons" on the Safe Mode start window to disable all extensions.

   Close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")''' "

worked for me, and I'm in Firefox 12! Thanks !

Please de-activate any extension that plays with proxy settings. I did so with "Stealthy" and now it works properly.

FF 12.0