Overly sensitive marking

[Cinderbella]

I've noticed that when I attempt to mark a puzzle, I get anything from the wrong mark (O instead of X) to the pop-up window admonishing me. This seems to have increased and is annoying as all hell. I'm on Firefox, the newest version (to date). I wish I could provide more information, but there doesn't seem to be anything consistent with when/where the errors occur.