How to Make Gmail Your Default Client in Firefox 3
The Official Gmail Blog explains how you can make Gmail your default e-mail client (meaning Gmail will launch whenever you click an e-mail link) in the recently released Firefox 3 browser.
It's a pretty simple process: All you do is sign into Gmail, paste a snippet of code into the address bar, and follow the resulting prompts. See the original post for complete instructions, and make sure to follow step 4 closely.
Definitely a useful tip for Gmail users who've made the move to Firefox 3.