Lifehacker has a great post on tips and tricks for Firefox 3. Favorites include deleting mistyped URL’s in the new URL suggestion window and auto-complete entries (I hate when my mistakes get saved!), making web applications like gmail launch instead of default desktop apps, enabling spell-checking in single line input fields (as apposed to just textareas), and lastly, for Mac FF3 users with the default Safari skin, adding favicons back in your bookmark toolbar.
navigator object called
registerProtocolHandler . For example, registering the mailto protocol to your gmail looks like this:
This has some really exciting potential for web apps!