Unfortunately it's impossible to reply to this thread: [https://support.mozilla.com/tiki-view_forum_thread.php?comments_parentId=365472&forumId=1] although the problem described there isn't solved at all. Quote from the OP: ''"Firefox is only checking the resolution of the primary monitor when it is opened or when a new window is opened. This is not an issue if both monitors are the same resolution or if the primary monitor is set to a higher resolution than the secondary monitor. But, as in my case, if the primary monitor is set to a lower resolution than the secondary monitor, Firefox will resize any new window that is larger than the resolution of the primary monitor down to size of the primary monitor."'' Personally, I have been using MSIE 6.0 until it became unusable since any major site stopped supporting it. Now, instead of upgrading to 7.x or 8.x, I chose to install Firefox ... and the first thing that this "state of the art browser" is giving to me as a welcome present is the insight, that it is even too dumb to remember its actual default window size! Although stored correctly in ''localstore.rdf'' (height="1170") this friggin bastard resizes to 994px height on every startup and refuses to accept the fact that the screen it opens on has a height of 1200px. Something the good old MSIE didn't have any problems with to recognize! Conclusion of > 1 hour online research: no solution available. Well done, Mozilla, brilliant job :\