Nerd Tip of the Day: Firefox Not Saving Cookies?
I recently had this problem, and found the solution after a little Googling.
You might notice that sites that used to auto-log in, like your webmail provider, now require you to manually log in each time. Your login information is stored in cookies, and this likely means that Firefox’s cookie file is corrupted.
Navigate to the following folder (in Vista):
C:\Users\[Your User Profile Name]\AppData\Roaming\Mozilla\Firefox\Profiles\xxxxxxxx.default
Put your Windows user name in the first blank. The actual folder has a randomly-generated name, something like “5gjbzh6p.default”, but you most likely only have one of them. You’ll need to have Explorer show hidden files and folders, as the “AppData” folder is hidden by default. (In Vista, the setting for this is in Organize->Folder and Search Options->View->Show hidden files and folders.)
Inside that folder is a file named “cookies.sqlite”. This is the corrupted file. Rename the file to something like “cookies.backup”. (So that we can restore the file, if it turns out that this wasn’t the problem after-all.)
Open up Firefox, log in to your favorite website to set your cookie. Now to test if cookies are saving correctly, close Firefox, re-open Firefox, and go to your favorite website again: you should be automatically logged in.