There is software like Advanced SystemCare with its Surfing Protection feature that can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

See also:

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

I don't have this type of software that I'm aware of (Advanced System Care). What should I check next?

Did you check the prefs.js file in the Firefox profile folder like in the link I posted above?

I will remove the solution that you set on my first reply as you still have the issue Make sure not to click the solution link in the email to avoid confusion

There is a file prefs and an Invalidprefs file. should I rename it prefs.js?

Try to delete both prefs files in case that is (or has been) a problem with the file.

Note that Windows hides some file extensions by default. Among them are .html and .ini and .js and .txt, so you may only see file name without file extension. You can see the real file type (file extension) in the properties of the file via the right-click context menu in Windows Explorer.

I deleted both of the files, what next?

Do you still have the themes disappearing?

Data of currently installed lightweight themes (Personas) is stored in the lightweightThemes.usedThemes pref that you can inspect on the about:config page, so problems with the prefs can cause you to lose such themes.

You can make a backup copy of the prefs.js file and compare this backup copy with the file in the profile folder after rebooting the computer to see if there are changes and compare the time stamp of the file as well.

After deleting both files, I closed out all programs, and re-started the computer, when it came back up and I went into Firefox I had the default theme (I expected this since I deleted the prefs files) I reselected my chosen themes and, then shut it all down again, when I came back to Firefox the themes where gone once again...grrrrr

Did you create a backup of the prefs.js file?

You can use this button to go to the currently used Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)

How do I create a back up of the file, I tried to copy and paste it to a new folder in my documents, but I can't open it, nor can I open the original file, well that's not exactly true it flashes open and closes again almost immediately.

Do not double-click the file, but use "Open with" in the right-click context menu to open the file in a text editor like Notepad.

You can copy the file to another folder or let Windows create a copy with a number appended to the name in the same folder.

Okay it's on notepad..

You would have to check the user_pref("lightweightThemes.usedThemes", <pref data>) line to see is anything got changed in the data that stores installed lightweight themes and compare this line in the current prefs.js file with the corresponding line in the backup of the prefs.js.

Cor-el;

   I just wanted to say thanks for all your assistance, the problem is now resolved, I ended up removing  2 recent extensions, both of them Facebook related, the last one I removed was the culprit it turns out..lol I guess I didn't need those hidden emoticons anyway. :) After removal I re-added my themes and then restarted the computer, and what to my wondering eyes should appear, but my theme right there up top where I left it. I'm going to re-add the other extension again and see what happens, if my themes disappear again I'll know there was something from each extension that was affecting my prefs.js file, but I'll be able to repair it again knowing what caused it. :) Thanks again you've been wonderfully patient with me...