Wow, version 30.0 already. I understand they recently (well, a few years ago) changed their versioning system. I wonder if we'll see another change soon given the version #, or if they'll just keep going.
In any case, the only bug I've had with FF lately is if I download something, Windows 8 notifies me that I cannot move the file, etc, from its Downloads directory as it's already in-use. This does not go away until I close Firefox, even if I clear completed downloads within FF. This may be similar to the already running message you mentioned.