If I open 66 first, it opens all the tabs from the last time I closed it. If I then open 63, it only opens one tab. So maybe I should open 66, then uninstall 63?

Firefox comes in three or more folders on all computers. They are;

Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And two folders in the profile of each user on the computer for each Firefox profile for that user.

If you remove the Firefox folder, the user profiles would not be affected.

It looks like both programs are accessing the same profile.

This is what you can do. Open the file explorer on your computer. Make your way to the OLD unwanted programs folder and remove it.

After rebooting the computer, run a registry scanner if you have one.

I have had this same issue before, the way I use to solve this type of problems is using windows control panel then look for uninstall programs and uninstall the version you do not use. Caution: before doing this make sure you have a backup of your profile, then restart the computer. Reinstall the desired version of FF from mozilla.org and import your bookmarks and profile or sign in to synchronise to the mozilla foundation sync service.

If the problem persists, what you might need is to uninstall again and delete all FF ledges that exist under windows program files directory. Then repeat the afore mentioned procedure.

You should always confirm in such cases that the two versions are actually installed and that this is not about a leftover key in the Windows Registry that wasn't removed by the updater. In that case only one Firefox version is installed and removing the older version will remove the current release as well.

How do I check that? Can you give me step-by-step directions or tell me where to find them? Thanks.

In Control Panel>Programs and Features>Uninstall, it shows

Mozilla Firefox 63.0.3 ((x64 en-US)...Mozilla...3/0/19...169 MB...63.0.3

Mozilla Firefox 63.0.3 ((x64 en-US)...Mozilla...4/11/19..175 MB...66.0.3

That would be inspecting this key in the Windows Registry with the registry editor and check Mozilla Firefox keys.

• HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\

Using the registry editor, it shows:

Mozilla

Mozilla Firefox 
  -66.0.3 (x64 en-US) 
  -- Main
  -- Uninstall 

mozilla.org

-Mozilla
  (name)                (type)               (Data)
 (Default)              REG_SZ                  (value not set)
 CurrentVersion   REG_SZ                   66.0.3

So I see no entry for 63.0.3.

There's also this:

Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\Mozilla Firefox 66.0.3 (x64 en-US)

There should be a key present that shows the installation path of each item. If the installation path is the same directory for both Firefox versions then it is likely a leftover key and you can remove this uninstall key.

I don't see 63.0.3 anywhere. Where should I look?

If there is no key for Firefox 63.0.3 then you can ignore it. You can check if there is a similar key in HKEY_CURRENT_USER.

• HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Uninstall\Mozilla Firefox

Yes, it's here!

Computer\HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Uninstall\Mozilla Firefox 63.0.3 (x64 en-US)

Now what?

If there is a path key present then you can check its value, otherwise you can probably just remove this key because this Firefox version got installed as a user and the updater may only be checking the keys in HKEY_LOCAL_MACHINE and not in HKEY_CURRENT_USER.

How do I check its value? Like I said, not an expert!

Does that explain the two icons and the two entries to uninstall the program?

Yes, that is the most likely explanation for seeing two Firefox entries in the Windows Control Panel. We regularly see questions about seeing multiple Firefox version showing in the Windows Control Panel Programs section and this is always caused by the updater not having removed the entry for the previous version unless there is a 32-bit and 64-bit version installed in different folders.

So to be triple sure I'm doing the right thing, just delete:

Computer\HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Uninstall\Mozilla Firefox 63.0.3 (x64 en-US)

(I get nervous when I do something in the registry!)

That should do it?

Did you check that this version points to the same installation folder as the other version?

You can export this key just to be sure before removing it.

Display|con:

For 63:

C:\Users|Frank|AppData\Local\Mozilla Firefox|firefox.exe.o

For 66:

C:\Users|Frank|AppData\Mozilla Firefox|firefox.exe.

 -----------------------------------------

For InstallLocation

For 63: C:\Users\Frank\AppData\Local\Mozilla Firefox

For 66: c:\Program Files (x86)\Mozilla Firefox