Resolved. The Reset Firefox made the false version report disappear. Btw, this version of Firefox restores itself back to the previous configuration after the reset. No need to reinstall your extensions.
You're right. Something is wrong. I disabled all my 3 extensions (Roboform, Track-Off and FAcebook Container). Shut down Firfox. Opened it up clean. Tried to install Malwarebytes BRowser Guard. Same message.