rogergr311049, you can sometimes legitimately have two instances of Firefox installed, when they are a different "edition". I do not believe that you can have two instances of the same edition installed, even if they have different version numbers.

For example, I once had both the 32-bit and 64-bit stable release editions of Firefox installed at once. You can, I believe, also have both the stable release and developer's editions installed.

So I would suspect that you have two different editions installed, rather than having the same edition but with different version numbers.

Are you sure that both installed Firefox applications are 64-bit? Normally only 32-bit applications are installed into the Program Files (x86) folder.

When you normally launch Firefox, what edition / version does it state in Help menu / About Firefox?

Are you able to launch both your installed Firefox applications (with only one running at a time), and see how they describe themselves in About Firefox?

Finally, I fixed the issue by myself.

The fact that I had two copies of Mozilla Firefox on my PC was due to the existence of a second Windows account which I created some time ago.

Also, in this second account, I had installed a copy of Firefox which was settled down again in "C:\Program Files (x86)/Mozilla Firefox" creating all this issue.

From the second account, I removed Mozilla Firefox and that's all.

Anyway I thank you all, who deal with this problem of mine!

JOHN HATZITOLIOS