in the URL bar I suddenly got stuck with a bubble of A versions that kept repeating until I restarted my iMac.
I was entering an URL in the location bar at the top. after typing the "a" I got a pop-down bubble with various foreign language versions of a which would not close. I finally clicked a version of a, then the a started endless repeating. Forced quitting of Firefox didn't stop; the forced quit box was troublesome and then the a's started endless repeating in NeoOffice. Logging out of my account didn't help; then the a started repeating in the password field. I finally did a restart to get my system back.
Opaite Mbohovái (1)
Sounds that the 'a' on your keyboard got stuck for some reason. Sometimes it helps to press such a stuck key a few times. Otherwise you may have to reboot the computer.