Why are mailto links not clickable in Firefox?

I had the same problem with the latest version of Firefox (2.0) on my Mac system too, and it took me quite a bit of digging to find out what was going on and how to fix it. The problem is that the somewhere along the way, the binding of what application to hand off email links has been severed or broken. So it's not that the links aren't clickable, just that they don't "go" anywhere.

Worse, this vital function can only be tweaked by digging into the guts of Firefox, it's not something that you can modify - or even check - by going to the Preferences area of the web browser. Even if it should be there (hint hint, Mozilla team)

The fix involves learning something very cool about Firefox nonetheless. To start; you need to open up about:config (that is, literally type that into your browser location window, or choose File --> Open Location and enter that.

Now you'll see a long list of system settings and values:

On the top of the window a new "filter" option appears too. Type in "mailto" and it'll filter all of the config settings to just show you those that are related to your mail configuration:

All the entries with "Google" as their preference are produced by the installation of the Google Toolbar (you knew toolbars had to get hooked into the system somehow. Now you can see).

What you want to do now is right click (or Control+Click) anywhere in this window, which will pop up a contextual menu. You want "New" --> "String":

For the name of the new string (the prompt is actually for "New string value: Enter the preference name") enter network.protocol-handler.app.mailto and click "OK"

Next you need to enter a value for this string. I use Microsoft Entourage 2008 as my email application, so a bit of digging around (use Spotlight to speed up the process, if you'd like) reveals that the actual Entourage application lives at "/Applications/Microsoft Office 2008/Microsoft Entourage". That's the value I type in:

Click on "OK" again and you should now be setup and ready to go.

If it doesn't work, you might also find that you have litter from a previous installation of the Google Toolbar getting in the way. Look for "google.toolbar.mailto.default". If that happens, try reinstalling the Google Toolbar and then uninstalling it.