Hi, rack88, bigwebb83 and beast m0de, welcome to the Seven Forums!
I dunno, guys. I've been using FF x64 for quite some time now (4.0b8pre, currently) and have never seen this issue.
Have you tried starting FF in safe mode or with a new (test) profile? It might be an add-on, extension or plug-in that broke with the latest updates. To root it out you will have to disable them one at time until the issue goes away; then you'll have found the culprit.
If all else fails, uninstall FF (your bookmarks and settings will be saved unless you specifically indicate you want to delete them) and do a re-install.
BTW, as far as the "Mixer," FF doesn't show up specifically but the plug-in does: