in 6.1.1.1100 mx hotkeys override those of the websites you visit. for example, i've set F2 to be the "previous tab" hotkey, and now i can't edit formulas in google sheets using the same F2 hotkey.
it was fine in mx5, so had to revert to it, albeit the new mx6 branch is far better in other ways.
oh, and one more thing: mx6 doesn't start without administrator rights on win10x64.