I recently switched computers from Windows 7 and very old version of Firefox (48 IIRC, there were reasons, but these are not relevant here) to Windows 10 and the latest Firefox release.
The one hard-trained UI reflex that I can't get used to is that in my old setup when navigating forms a single press of the tab key could select the currently highlighted choice option in a dropdown list and switch to the next element. Now switching to the next element requires two presses of the tab key: one to select ethe highlighted choice and close the list, and a second one to actually switch to the next form element.
I strongly suspect it's a Windows thing rather than a Firefox thing because Chrome displays the same behaviour, but I have no idea if there is any hope because any attempt at searching for a solution is overloaded with question about navigation tabs (thanks, Google </sarcasm>).
