Follow up
Fixed the login problem, after checking the "Advanced" tab in IE. Turns out the thing to do is uncheck the "Use TLS 1.0" box, which is checked by default when Firefox installs.
Now I have to figure out why opening HabZone makes the Firefox status bar go away... annoying, but not critical.
And you're right - no "HTML preview" available here using Firefox. A couple of extra buttons are missing, too. Hey, Robert....