I have been using Iceweasel 3.6 from the Mozilla Debian repositories to get the newest security updates for Firefox/Iceweasel. With the release of Firefox 4, they have added Iceweasel 4 to their repository. The new version requires a higher version of libcairo2 than what is available in the Debian testing repositories (or the version provided in the LMDE repository), so they have included a new version of the library to be installed alongside Iceweasel 4.
It looks like the version of libcairo2 included in LMDE comes from Ubuntu and I'm sure Clem included this specific version for a reason, I just don't know what that was. What I am wondering is, what would I lose installing the Mozilla Debian version that wouldn't be included in the one Clem included in LMDE?