There seems to be a issue with Firefox 4.0 and the buttons next and save and next.
You see those buttons when you are editing settings for things like Virtualmin Config, postfix config and template config.
What happens is when you click on those buttons it only works once after that you are stuck and the window frame does not advance to the next config section.
Not sure if anyone else has seen this. I also tested with Konqueror Version 4.4.5 (KDE 4.4.5) and this didn't happen.