Firefox only (Windows/Mac/Linux): Whenever you hover over a link, Firefox extension Status Address Bar displays the URL a link is pointing to in your Firefox address bar, eliminating the need for your status bar and freeing up precious screen real estate.
For many, the only reason Firefox's status bar is even useful is so they can see what URL a link is pointing to before they click it. If that's the case for you, those extra 14 or so wasted pixels at the bottom of your browser window are probably better suited for adding a little more height to your browser's viewing area. The Status Address Bar gives you the best of both worlds:
With this extension installed, you can hide your Firefox status bar (View -> Status Bar) and still see where links are pointing — only rather than displaying the URLs in the status bar, Firefox will display URLs when you hover over a link in the Firefox address bar.
In the screenshot, for example, my mouse is hovering over the article headline and its URL is visible in my address bar. It's not groundbreaking, but if you're looking for more ways to maximise Firefox's viewing area without sacrificing functionality, it's a nice addition. Status Address Bar is an experimental Firefox extension, works anywhere Firefox does.