I would not do a system restore, it can cause problems. Also a system restore is unlikely to restore the bookmarks.

The lost bookmarks article may help.

Thanks, we have managed to restore the bookmarks from bookmarkbackups but not had any luck with passwords.......the latter we can build again.

Ok, by copying the files key3.db and signons.sqlite from my old directory under profiles to the new directory created today and overwriting those in that directory I managed to get the passwords/usernames working again.

Not sure if anything else does not work at the moment but looking good......

Now I realise all my of add-ons have gone as well!

It sounds like a new profile was created. Firefox stores user data in a profile, if a new profile was created it will be like starting afresh with no bookmarks, password, add-ons etc. Try running the profile manager, if more that one profile is listed try switching to the other profile. For details on how to do this see the managing profiles article.

Exactly, we all have to login in to our machine and recovered some files from the previous profile:

C:\Users\xxxxxx\AppData\Roaming\Mozilla\Firefox\Profiles\x3e3z89z.default\bookmarkbackups\

Thanks I will look into this......

One week on and I have had this fault again, however this time my old accounts have gone....no bookmarkbackups or profile to view and copy!!!!

I installed 3.6.12 update and the program ended up in Safe Mode somehow. It dumped all the tabs I had saved, but all of the bookmarks remain intact. However, now it has "Run this program as an administrator" turned on . I turned it off in all the places I could find but it still insists on being run as an administrator. The selection is greyed out under "compatibility" but shows it checked (on). If I go to change for all users, it is unchecked. I tried checking it, and pressing "apply" then unchecking and pressing apply but it won't go away. Every time I load the program as a non-admin, it asks for the administrator password saying that Firefox is going to change the computer.

This really sucks!

@ian2465

"copying the files key3.db and signons.sqlite from my old directory under profiles to the new directory created today and overwriting those in that directory I managed to get the passwords/usernames working again."

THANK YOU!!! I would have been beating my brains out thinking of all my lost passwords, & that saved me. Add-ons not such a big deal, if I miss them I can find them again, & often they're not compatible with the upgrade! This will teach me to back up regularly, because I had NO idea the upgrade to 4 would be so traumatic!