When you are trying to share the same Firefox profile across different platforms (such as Windows or Linux) or across different versions of Firefox, you will see a warning – “You’ve launched an older version of Firefox“. The message goes on to explain that using an older version of Firefox for the same profile might corrupt the bookmarks, browsing history and other files already saved in that profile. It suggests that you create a new profile and won’t let you proceed with the same existing profile. At this point you can click on “Exit” and dismiss this message or create a new profile.
The problem with sharing profile with different versions of Firefox or different platforms is that browsing history is saved in a different manner and trying to load them on other setup might indeed cause some problems. But before you create a new profile, you can make an attempt to use the same profile in the following manner:
- Make backup of your Firefox profile using MozBackup. You can also manually copy the profile folder somewhere else to backup it.
- Launch Firefox in the working platform/version setup.
- Enter about:support in the address bar.
- Locate Profile Folder and click on Open Folder button.
- Close all Firefox windows.
- In the folder that opens, double-click on compatibility.ini and remove all of its content. Save this blank file.
- Right-click on compatibility.ini, select Properties, select Read only and click on OK button.
- After this Firefox won’t show any warning when the profile is shared between two different versions.
If you are sharing the same profile between Windows and Linux, then you will have to make similar changes on Linux to ensure that compatibility.ini file inside the Firefox user profile is read only. Usually, this is done by giving a shell command chmod a=r compatibility.ini or through the user interface of the file manager for a specific Linux flavor.
This won’t work if you are using Firefox through Administrator user account in Windows or root user account in Linux, because then any file “read only” permission has no meaning. If this does not work or causes profile corruption, then you can restore profile using the backup that you had earlier created.
Alternative workaround is simply to add the parameter “–allow-downgrade” to the command line in the shortcut.
This is a life-saving article!!! Firefox team always neglect their users so it’s the only solution when you’re reverting to previous version..
Thanks a lot, this solution worked for me on Linux Mint 20.1, Firefox 89.
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