if you're talking about ie, you need to be in f11
my ie lauches to f11 by default by the way.
anyway, once in f11, just right click on what's left of the toolbar, and autohide presents itself.
if you're talking about mozilla, it's only available in pheonix, and again, f11, but I forget where autohide is in the pheonix gui.
noww, check this out...this is a post that I wrote for the front page a while ago;
If you're like me, you like as much content on your browser page as possible.
The best way to do this is by hitting the f11 key, which will give you a full screen.
You can increase this screen size even more, by auto hiding the task bar on bottom, and auto hide the toolbar on top as well.
If you're not familiar with how to do this, simply right click on the toolbar on top while in f11 mode, and the option to autohide presents itself
On the task bar on bottom, find an empty area again, right click, hit properties, and there is the option to autohide this bar as well.
Now, I like as much content on my browser page even when I'm not in f11 mode, and with a few clicks, you can usually bring all of the buttons and functionality of your toolbar to one bar, without loosing any of the functionality!
First, right click on the toolbar, hit customize...
The first thing you should do, is hit "no text labels" on the bottom...by now, you should know what all of the icons do without needing the space consuming text labels
Now, if your vision is fine, you should also hit "small icons" in the icon options box...this will also make better use of allot of wasted space.
alright, now go to the icons box on the top right, highlight and remove every button that you have not used in a while.
This will usually include the printer button, which usually does not work, the home page icon, which most people almost never use, and every other button you think is unnecessary for your personal use.
You should also eliminate all of the separators, as they serve no purpose at all
Now, for the best part;
Close this box, and go back to a right click on the toolbar again, where you will uncheck "lock the toolbars"
Go to the bottom left of the toolbars, grab the dotted lines that are now available, and drag each one to the right and up one level.
You should now be able to get all of your functionality onto one toolbar.
This will include the address bar, which for most users does not need to be bigger then an inch and a half or so of the toolbar.
When you're satisfied with your new toolbar, go back to a right click, and lock the toolbars again.
There...now, you will enjoy almost f11 viewing, but you will have all the functionality of a full toolbar.