Try disabling zooming with the mousewheel while holding the Ctrl key, by changing mousewheel.with_control.action to -1 in about:config.

I just noticed that i suddenly have the same problem. Pressing the Ctrl key -- even without pressing any other key -- automatically zooms out the page and brings up a % icon in the address bar to indicate the current zoom level (30%, 50%, etc). I want to be able to use Ctrl codes without this occurring; how can I disable it?

Hi borisgoodenough

Did you try to close and restart Firefox or reboot as that is usually the first to try in case of weird issues?