Also, if you guys don't have "Web Developer" installed, I'd suggest it. Even for just doing html pages, ti's a huge help... one of the features, for example, is a "resize window" option where you can tell it width and height and it resizes the window to it.
So you can check your designs in various sizes, or... should something sneak through and resize your browser somehow again, it's a quick button press to get it back to the way you like it.
https://addons.mozilla.org/en-US/firefox/addon/60