**Firefox-5.0 was just released as 'stable' by Mozilla (yesterday) ... and has already hit the repros.
And me, always wanting to be on the 'cutting edge' of Open Source ... I have just installed Firefox-6.0 Aurora A2 from the Launchpad.net/mozilla PPA's. (remember PPA's work with Ubuntu-based distros and do not work with Debian/LMDE)
Launchpad.net/Mozilla PPA site > https://launchpad.net/~ubuntu-mozilla-d ... fox-aurora
Firefox-6.0 Aurora is to be released in Sept. 2011 ... and, is now available for testing and bug-reporting purposes.
But for Debian/LMDE you can get Iceweasel:
# Iceweasel 4.0/5/6 beta/aurora packages for Debian http://glandium.org/blog/?p=1032
# Debian Mozilla team APT archive - http://mozilla.debian.net/
# To use this archive, you need to add the following entry in /etc/apt/sources.list
# deb http://mozilla.debian.net/ $release $pkg-$ver