This is a Firefox forum, not an Operating System one. I would just search around for good Linux Distributions (I've used ubuntu and Kubuntu before, enjoyed them both)

http://distrowatch.com/table.php?distribution=linspire
You might want to look at a distro which is more up to date. Linspire 6.0 was released almost 5 years ago. Five years in the Linux world is like 12 or more years in Windows years, IMO. Changes and improvements come at a quicker pace.

The Ubuntu distro, and its off-shoots, usually release a new version like twice a year, and the LTS (long term support) version is new every two years.
http://distrowatch.com/

The biggest issue with using a old Linux distro version like Linspire 6.0 will be meeting the minimum package version dependencies for various applications as per ones like mentioned in http://www.mozilla.org/en-US/firefox/15.0/system-requirements/

Lots of more current ones like openSUSE, Ubuntu, Xubuntu