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I would like to revert Firefox to a previous version and keep it that way.
I understand that the developers don’t want users doing this.
I have tried simply uninstalling and re-installing the proper version (their instructions here), but when I try to start Firefox afterwards, it prevents me from importing my profile. Firefox does this if the profile is newer than the installed version. In this question, I am asking how to revert and maintain my profile.
I have searched Superuser but don’t see an answer. This answer is about old profiles; my question is actually about profiles newer than the installed version. This answer is also about copying an older profile. This answer is about going from 32-bit to 64.
These instructions are for Windows, but the ultimate solution (which is adding
--allow-downgrade to your startup shortcut) is the same for Linux. These instructions are basically all about getting a clean install, using that flag to start, and turning off updates.
Locate your Profile folder and make a note of its name and location. On Windows it is at
%APPDATA%MozillaFirefoxProfiles. It will have a name like “nr4vrqj6.default”. Later you will have to copy it to the new install.
You can get to this folder from Firefox by going to Hamburger menu->Help->Troubleshooting Information->Application Basics->Profile Folder->Open Folder.
Download the version of Firefox you want. The previous version is on this page. A directory of all previous versions is here.
Uninstall Firefox. There may be associated pieces of software with it, also called “Mozilla Firefox (name)”, like the updater. Uninstall those too.
(The first time I tried this I did not completely uninstall Firefox and reboot, and it turned out Firefox 88 was actually still installed. The About menu said 86 was installed, but on the Windows list of installed programs, it showed Firefox 88, and it still acted like 88. Possibly you can just uninstall Firefox properly and not have to reboot like I did, but browsers get their hooks deep into everything.)
Install your chosen Firefox version (in my case 86, the one prior to 88). Don’t start it yet. If you accidentally start Firefox, you may need to reboot again after this step.
Locate your new profile directory. It will be in the same directory as the old one and also have an unpronouncable name. Copy the contents of your old directory to the new one, overwriting anything there.
Firefox cannot be running when you do this, and in fact I was forced to reboot again before doing it, because Firefox had left some process behind that was still preventing the clean copy. Firefox tries to do everytihng it can to prevent you from doing this.
Go the the Firefox shortcut on your desktop, and edit it. You need to add the flag
--allow downgradeat the end. Linux users would likewise add this flag on the command line. Without this, Firefox will block you from opening it when it sees a profile from a newer version.
Start Firefox using your new shortcut. The very first thing you need to do is turn off automatic updates! Go to about:preferences -> Firefox Updates, and turn off automatic updates.
Whenever you start it for the first time, turning off automatic updates should be the first thing you do.
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