Steer clear of upgrading your Firefox to Version 3.5 if you can. I had a heart attack by the time I came to the conclusion. On the face of it, 3.5 was just amazing. It fixed most of Firefox 3.0 's loathsome browser like frequent crashes, inability to surf websites like Youtube and crashing under particular conditions such as clicking the back button on Yahoo Answers or searching using the search bar.
Now to the downside, Firefox 3.5 has grave problems that seriously undermines confidence of consumers in open-source browsers such as Firefox. For starters, it gets choosy and doesn't remember all the saved passwords !
After upgrading to Firefox 3.0 in the beginning of the year, the experience was horrible. I was such a fan of Firefox that if there was a 'Firefox religion' you could me a priest,fanatic, whatever. You get the picture. The main attraction of firefox was it's speed, the ability to open multiple tabs and surf much more smoothly as compared to the sluggish Explorer. Firefox 3.0 was not only extremely slow, it also crashed on various websites including Youtube and TheFreeDictionary.
However, once I tried to logon to Gmail, horrors of horrors ! Firefox was unable to enter any of my Gmail passwords, but to my bewilderment, retained passwords of other sites. It turns out that if you upgrade from a pre-3.5 version, some mix-up occurs with the passwords list and only some of the passwords are successfully migrated to the new browser. However, if this has happened to you don't panic. You CAN RECOVER IT.
Bluntly put, you need to install a pre-3.5 version of Firefox. Then you can access all of your previous passwords. As simple as that.