(my default firefox settings are occidental iso 8859-1, no automatic detection, unicode utf8 encoding).
i have the same Version of FF an the same settings. i tryed to deaktivate all addons without any changing.
Then i also make a test with this side with IE 7.5730.13 an get the same mistake

The IE shows the sidecode in the header without login is charset=UTF-8 an everything is ok
After login the sidecode is charset=ISO-8859-1 with the wrong umlaut
Whats going on there ?