Hmmm... after you installed the plug-in, did you re-start your computer? Also, make sure you deleted all your cookies... that usually is a problem for most people (I think you can do that on Firefox too). You may want to re-install Firefox as well... when I have used Firefox, I usually don't have a problem with logging in, so try these things and hope they will help you out! 😊 If not, feel free to PM me.
Topic closed.