Okay. While you can have as many versions of Firefox as you want on your system, it is Required that each has its own profile. Also, if you want to use an older version, you will need to disable the browser from updating. As this is no longer possible via the settings, you will need to create a 'policy for its profile.

You can use sync to share passwords, bookmarks, and history. Anything else may not be compatible between different browser versions or computer systems.

If you are confused or don't understand the instructions, Stop and ask.

Follow these instructions to install the version you want. HOWEVER, at the end, the installer will ask if you want to start the browser. Answer: NO ! ! The reason is it will open using the current profile and this could cause issues.

Note: With some versions of Firefox, the data files are not backward compatible. If there is an issue, create a new profile and we can tell you how to recover the data.

Install Older Version Of Firefox {web link} Be sure to read everything here.

If you still want to downgrade, look under; I still want to downgrade. Click the Directory of other versions and languages link. Look for the directory of the version that you want. But, remember that old versions may have security issues.

Note: If you know what version you want, press <Control> (Mac=<Command>) F to open the search bar. Then enter the version number to see the available files.

I forgot to add, during the installation, switch to the Manual option. Then you need to select a name for the Programs Folder for this version. Use something like; Firefox_ESR_v (whatever)

These are how my computer is set up; "C:\Program Files\Mozilla Firefox_Current\firefox.exe"

"C:\Program Files (x86)\Mozilla Firefox_54\firefox.exe"

Once you have installed the browser, you will now need to create a new profile for it to use.

Do Not just open the browser. It will try to use the current profile and this can cause issues.

Using the computer's file browser, go to the Programs Folder where that version is located. Go into that folder, right-click on Firefox.exe and select Create Shortcut. Move that shortcut to the desktop. Now right-click on the shortcut and select Properties.

At the top of the window, select Shortcut. Look for Target.

At the end of the Target line, add -p. This will make the browser open the Profile Manager. Now you can run the browser using the shortcut. From here, create a new profile and make sure to give it a name. Use something like; Firefox_ESR_v (whatever)

I will continue with the instructions when you get this far.

Great! Works! Thank you :-)

Any problem so far?

Once things are set up, you can edit the shortcut for the ESR to go directly to that profile without going thru the Profile Manager.

Examples; "C:\Program Files\Mozilla Firefox_Current\firefox.exe" -p default-release "C:\Program Files (x86)\Mozilla Firefox_54\firefox.exe" -p Firefox_54