Preferences not saved
This article deals with changes to options or preference settings not being saved after you restart your Mozilla application. If Firefox toolbar customizations are not being saved, see this article.
Read-only or locked preference file
The inability to save any preference changes can be caused by having a read-only or locked prefs.js file or "prefs.js.moztmp" file in the profile folder. You may receive an error similar to "Failed to save the preferences file. Any preference changes will be lost at the end of the session" [1]. You may also find multiple files named "prefs-<n>.js" (where <n> is a number) in the profile folder. Check the file properties of the prefs.js file (and "prefs.js.moztmp" file, if found) and make sure that the "read-only" attribute is not set. You can also delete any "prefs-<n>.js" file copies.
Note that other software such as Dell Network Assistant may be causing the problem by locking or "protecting" the preference file. If you have this program, try disabling or uninstalling it [2]. See Multiple profile files created for more information about locked or multiple files in the profile.
User.js file locks certain preferences
If you are able to change some preference settings but not others, look for a user.js file in your profile folder (Windows users, read this for help finding it). The user.js file does not exist by default; it is created by users and, in a few cases, by some software programs, so that certain settings get written back to the prefs.js file each time you restart your Mozilla application If you find a user.js file, either remove it from the profile folder or edit the file to remove any unwanted settings. See Resetting preferences for more information.
Other solutions
- If you have a current profile backup you can replace the prefs.js file with the backup copy, in case the current file is corrupt.
- The Standard diagnostic provides a basic troubleshooting guide if the preceding suggestions do not fix the problem.
