Copy all contents of your stable version profile to the newly created profile.Don't start Firefox yet after profile creation.This displays the profile manager on launch that you use to create a new profile.

Run the development version with the parameter -p.The idea here is to create a second profile that you use for testing so that your main Firefox profile won't be altered in any way. If you want to be on the safe side, use the thorough method below or backup your Firefox profile using MozBackup or a comparable application first. Mozilla may make changes to the browser that are not compatible with the stable version. The main issue with this method is that you may run into compatibility issues when you go back to your own version of Firefox. This means that all of your add-ons, themes and customizations are included.Ĭheck if everything works and if it does, you are done. Load the installed test version of the browser.įirefox will pick up the main user profile automatically and load it.Close all instances of Firefox on your system.

You have two options, one that is fast and the other that requires preparation.

Test on older versions of firefox