It plays out like a Harlequin Romance for many a Mac user (especially web designers and developers): you have a fairly solid relationship with Safari, on a day-to-day basis. Despite your admiration for Safari's beauty and speed, though, the siren song of Firefox frequently seduces you away for extended romps, tempting you with a bounty of desirable extensions and themes. Personally, I've just decided to make my relationship polygamous, Safari for browsing, Firefox for web development.
The rub, though, is in the definition of the system's default browser; for me, there's no winning that war. I'm constantly launching browsers unintentionally, wishing my Mac would just figure out which application I want to handle a link with at any given time. George Brocklehurst has a solution, though, and I'm loving it.
Choosy is a Preference Pane (and accompanying helper application) which takes the place of the default browser. When you click a link anywhere outside of a web browser, it takes action based on your preferences: you can have it open the link in whatever browser is running (defaulting to your favorite browser if nothing is open), or you can have it always display a choice of browsers, among other configuration options. I set mine up to display the menu of browser icons every time, thereby ending the unintentional application-launching which stems from my need for multiple browsers.
Choosy is in beta, and it's got some issues. The biggest for me is its inability to handle multiple displays. That, along with every other question I had about its future development, is already laid out in the development roadmap. Choosy will be a paid application once it's out of beta, but beta testers who provide George with an email address will be getting a code for a beta tester discount. If your own browser infidelity is causing problems for you, give Choosy a try.
Fair warning, by the way: If you install Minefield, you'll lose Firefox from your Choosy browser list until you uninstall it. The ability to customize the browser list is on the roadmap (and there is a workaround -- editing the CFBundleIdentifier in Firefox's Info.plist to a unique value -- but that's not for the fainthearted), so hopefully that will soon be a non-issue.