This is one I keep forgetting to submit...
If I have the extension open, then minimize it, then forget it is open, then I attempt to log into a site, the MPW prompt prompts me for the MPW, but when I hit enter or click OK, it doesn't populate the form.
Either it shouldn't prompt me at all - or even better a little dialog telling me to close it if I want to use it - or it should work... whichever is easier...