You’ve got AIM, Google Talk, MySpaceIM, MSN, Yahoo!, and many other chat networks to choose from, each with their own IM client. (Some of which can be resource-hogging and full of advertisements. =( )
Instead of simply using each individual client, why not use one client to handle all of these chat networks at once? There are many clients that do that. A few of them are Trillian, Miranda IM, and, my favorite, Pidgin. (Digsby can also be used, and it has many other capabilities beside instant messaging, you have to be careful while installing it to uncheck any bundleware, so I’m not going to suggest using it, and I won’t link to it, either.) Click here for even more options.
As for Firefox add-ons, might I suggest FireGestures, an add-on that adds mouse gestures and various other shortcuts to Firefox, all of which are customizable. You could even set it up to direct the browser to a certain website by drawing a certain symbol, such as a G for Google.