Firefox gets installed first, great for general web browsing and web development. The following addons are a must.
Flashblock - Prevents flash from running on a web page without your approval. Instead of flash, a flash icon is presented in a box where the flash would be. Click on the icon to load that flash element if your wish. The plugin prevents all those nasty CPU hogging flash ads from running. But just clicking allows you to run things like videos just fine.
Firebug - A web page debugger. A must for anyone developing a web site.
Chrome is next. Each tab has its own thread and runs really fast. Great for using Google sites too. There is also a FlashBlock for Chrome.
Lastly, SeaMonkey gets added. This is the real descendent of the old Netscape browser and uses the same rendering engine as Firefox. An integrated browser with built in mail and web page creation tool. In addition, this browser supports profiles. So if you have multiple Google accounts, for example, you can run a separate instance of the browser for each account.
For example, a shell script like this will run a new instance of the browser:
/Applications/SeaMonkey.app/Contents/MacOS/seamonkey-bin -P profileName &