You should be able to:
Download Firefox -
http://www.mozilla.org/en-US/firefox/fx/#desktop
Install Firefox
Start Firefox
Let it import your favorites, etc
Tell it yes you want it to be your default browser
Extra Credit:
Go to Tools - Add-Ons - Get Add-ons
In the upper right corner, in "Search All Add-ons" - type Adblock Plus
Choose Adblock Plus (current version is 2.3.2) and click "Install"
Restart the browser (I think, it will prompt you if needed)
Nothing gets lost.