Since installing Firefox 3.6.3 I noticed that it kept clearing all login details and every time I started it up and went to a site, I had to re-enter my details which is tedious and annoying. Now I’m one who has Firefox set to clear certain things on close down, and had set these setting via Tools->Clear Recent History… and thought that these were the same settings that would be used when Firefox was closed.
The actual settings for this are found in Tools->Options->Privacy and if you have “Clear history when Firefox closes” checked, like I have, you must then click the “Settings” button. This brings up a different dialog box to the one mentioned above and by default everything has been checked. Uncheck “Cookies”, click “Ok” and all should now work as expected.