Choose Wisley for Mac lets you select your browser on-the-fly

[riso]

Brand new stuff for Snow Leopard: If you choose to make Choose Wisley your default web browser, clicking links in other programs -- for example your email client -- will cause a pop-up a window to appear which gives you the opportunity to select a specific browser to open the link with. This tiny application is very useful for those who are into web development to test their work or who need more than one default browser.

All you need to do is simply drag and drop your browsers into the application window. A maximum of 5 different browsers can be stored, and browsers you no longer need can be removed by dragging them out of the window. Mac OS X 10.6 Snow Leopard is required. Older versions are not officially supported and may cause system crashes.

Choose Wisely is Freeware

http://blog.tigion.de/2010/02/16/software-choose-wisley/