Rated 4 out of 5 stars

I have found a way for Linux Fluxbox users to get Firefox in a windowed Fullerscreen. I mean a normal Firefox window that looks like it is in fullscreen using Fullerscreen.

Open your ~/.fluxbox/keys file and add the two lines.
OnWindow Mod4 Mouse1 :Fullscreen
OnWindow Mod4 Mouse3 :MacroCmd {Fullscreen} {ToggleDecor} {MaximizeWindow}

Go to the Firefox menu and select “Reload Config” or just restart Fluxbox.

How it works
In Firefox, press F11 to go into fullscreen. Hold down the “Windows key” and left click anywhere on the Firefox window. You will now have Firefox looking like it is in Fullerscreen but will be able to resize and view other windows.

If you wanted the Titlebar to disappear as well, hold down windows key and press right click when in fullscreen.

TO EXIT:
If you pressed Win+left click
Just press F11 and Firefox will go back to normal.
If you pressed Win+right click
press F11. Then do Win+right click(you might need to right click twice)
This will give you back the title bar.

WARNING:
There is a slight problem with the tab bar. It might disappear. I get this problem using Tab Mix Plus with multiple tab rows. To get the tab bar back, exit fullscreen mode.

If your multiple tab row becomes just 1 row, you will need to resize the window to correct.

This extension is great, but I cant select what extra toolbars I want to view. The preferences has nothing for it(using Ubuntu 8.10).