Here's a handy trick to remember, especially if you're viewing websites on a small screen, or if you use extra toolbars that take up some of your browser's "real estate." For example, if you want to get the best view of the Wildlife Photographer of the Year 2012 page, you may need to have your browser go full-screen.

Here's all you need to do:

Press the F11 key to make the browser open up full-screen; then press the F11 key again to display it back to normal with all the toolbars visible again.

Here's a screenshot of my Firefox window (besides the regular Menu toolbar and Navigation toolbar, I've got Firefox loaded up with a web developer toolbar and a Bookmarks toolbar) before pressing the F11 key ...

... and after:

Bonus: this keyboard shortcut also works in Internet Explorer and Chrome web browsers.

source: How to make Firefox and websites go full screen, Mozilla Support website
photo credit: Dadado Gonçalves via stock.xchng