The button in the upper right is not the full screen button. With the button you retain your toolbars, it is just like moving the window edges to fill the screen.

• Windows 7 keyboard shortcut WinKey + arrowUP vs WinKey + arrowDOWN
• "Alt+SpaceBar" > "M" to maximize or "R" to restore

Full Screen is "F11" and is toggled on/or by its keyboard shortcut, eliminates toolbars in full screen mode. You can have selected toolbars show while in Full Screen mode with an extension or a style.

Since you are talking about dragging the window back into position having crossed the screen boundaries, you should see the following article.

• Resizing oversize window - MozillaZine Knowledge Base
  http://kb.mozillazine.org/Resizing_oversize_window
• You have Win7 shortcuts of WinKey+arrowLEFT etc to move and resize the window to left, restore, right and if you have multiple monitors moves to the other monitor in same sequence before returning.

Maybe I wasn't clear in my original post. The Firefox window expands to fill the entire display without any action by a user. This is not the same as the full screen mode obtained by clicking the square in the upper right corner, or the Win key + up arrow key, or the other full screen entered with the F11 key. It is just the normal display where multiple windows may be seen on the display, but with the Firefox window covering the entire screen.

I did verify that the F11 key works and that the Win key + arrow key works. The ALT + space bar combinations just give me an error beep.

Thanks for the response

In the link there are two extensions mentioned do you have either of those extensions.

I read the link, but I do not use those extensions.

Also, I must have hit the wrong keys earlier, because the ALT + Space Bar does work.

Thanks for the response.

See:

• http://kb.mozillazine.org/Prevent_websites_from_disabling_new_window_features
• http://kb.mozillazine.org/JavaScript#Advanced_JavaScript_settings

Thanks. I read the links and decided to disable the JavaScript option for resizing windows. If this cures the problem, I'll then have to try to determine if some unknown piece of software is the cause.

I'll return and post the results.

I still have the problem. Sometime overnight the FireFox window expanded to fill the screen, but when I checked the settings for JavaScript, the check to disable changing screen size was gone. I'll give it another trial.

I checked to box to disable JavaScript from changing the size of existing windows again and the window suddenly grew to full display size again. I verified that the check mark to disable resizing was still there.

I upgraded FireFox to 9.0.1 this morning and it seems that the problem with expanding to fill the screen is more frequent. This includes going from a minimized state to filling the screen without my intervention - specifically when reading email on Window Live Mail, the screen becomes all FireFox.