Comment 26 for bug 641300

Here's what I found:

The problem seems to be interference / competition between firefox's auto-complete (or it could be google's autocomplete, I'm not sure which service does this) and the firefox spell-checker. When I turn off spell-checking in the subject box when the problem occurs, the auto-complete shows and all is well. If there is no auto-complete (ie. I have not typed text start with the same word(s) previously), there is no problem.

To test this: Try is with a gmail subject box. Make sure auto-complete is on, as well as spell-checking. Type something you never typed before. Like '6tiksmkd'. No problem. Type something like 'Japan Tsunami" (or whatever you entered before) and the problem occurs. No right-click in the subject box and turn off spell-checking. The problem goes away.

Can others confirm if the same happens with them?