Open With is a time-saving Firefox extension that will quickly open the current web page in another of your installed browsers.

So if you're a web developer, say, and want to see what your site looks like in IE, there's no need to manually launch the browser and enter a URL. Just click View > Open with Internet Explorer (in Firefox), and an IE window will open to display the current page.

If the extension doesn't detect your installed browsers (or maybe you're using a portable build), it's easy to add additional entries.

Version 6.7.2 (Changelog):
    - Translation update for Hungarian and Polish.

Verdict

If you regularly have to view the same page in multiple browsers then Open With could save you a great deal of time