I have never felt the need to sandbox any of my browsers, Firefox (default) or IE8 (only used once in a blue moon) and the same for other browsers which I have tried periodically.
I run all internet facing applications, Browsers and email clients, etc. under restricted rights, using DropMyRights. This however is only available under winXP. By running using a limited user account would achieve the same thing (but not as flexible).
If you encounter malware whilst logged on as a user with administrator privileges the malware inherits those same privileges, which allows it virtually free reign to do as it wishes. Running using a limited user account or running your browser, etc. under DropMyRights greatly limits the potential damage by any malware that gets through your defences.
I also believe in having a robust backup and recovery strategy, so should you experience a problem (doesn't have to be virus related) you can employ that strategy to recovery from the problem. I use drive imaging software that exactly copies a partition/drive, etc. and run it weekly.
If I have a problem that is likely to take longer than 30 minutes to resolve, I restore my last backup image, which takes less than that time. I then restore any backed up volatile data files (downloaded files, .doc, .xls, emails, etc.) which I backup at least once a day. So no real loss at all and it means not having to employ another application to sandbox my browsers.
