'''IF''' you install a new version of Firefox '''and''' uninstall an earlier version do NOT use the option to delete settings (or however that is worded) because that will remove bookmarks and other profile details from all installed versions of Firefox. Firefox will try to retain your settings including bookmarks, pass words and logins. Normally all you need to do is use the option on the Help menu to upgrade. * use''' Help -> About Firefox -> check for updates''' * see [[updating firefox]] * you may also be interested in [[common questions after updating firefox]] Often users set Firefox to upgrade automatically, and this is becoming more important now because new versions will tend to be released about every six weeks. Firefox 3.6 is still supported at the moment, but Firefox 4 is no longer supported, the current Release is Firefox5. What you should be doing is upgrading to Firefox 5 not Firefox 4. (The two are very similar, mainly the difference is with security fixes and memory handling improvements I understand)