Having Firefox 5 final version released with some minor improvements from Firefox 4 but the only problem you may face is some add-ons worked in Firefox 4 may not compatible with Firefox 5  and if you don’t want to sacrifice your favorite add-ons for Firefox 5 here is the guide to ( help you to get back to Firefox 4 without loosing your settings, bookmarks, add-ons which is called downgrading) downgrade from Firefox 5 to Firefox 4 or earlier versions .

Downgrading from Firefox 5 to Firefox 4.0.1 or older versions

1. Visit Mozilla FTP Server in your browser.

2. Open Firefox 4.0.1 folder  >Win32 folder >en-US

3. Download and install Firefox setup 4.0.1 exe file

You’ll be automatically downgraded to Firefox 4.0.1 and your favorite add-ons, bookmarks and settings will remain untouched and disabled add-ons will be enabled.

You can downgrade to Firefox 3.6.x by downloading latest Firefox 3.6.18 version from here.

Note :  You need to disable update checking for Firefox to stay on Firefox 4 or Firefox 3.6.x by opening  Tools> Options>Advanced>Update uncheck for “Firefox” for automatically check for updates to” option.

Update 21/06/11 : Post updated.