I will echo what Iamnothere said - I HAVE been tantalized into downloading the 1.7 version of Java because I wanted to not have to keep enabling the plugin or respond to whiny error messages or certificate warnings for every AMO. I uninstalled 1.7 and went back to the latest release of 1.6. It was also after that I noticed in the firefox "You have to activate the plugin" whine message that there was a box that says "always activate Java for this site" which cured my whining problems. I have also gone into the browser settings and told it not to whine about the certificate mismatch and a few other things...
Yes, I use Firefox to admin my 4000 (V5). I can't stand internet explorer, and firefox works just fine if you go through all the config steps while in firefox and ignore the whiny messages about browser versions. I actually like the way it drives much better in there. It's also nice that in Firefox you can add a certificate exception for the certificate mismatch error and it will never ask you about it again, rather than in IE where it asks every time, and turns the whole URL bar red to warn you that you're on an insecure site, etc...