A couple of questions on Debian
 

Hi

The last time I've used debian was in the early 2000s. I've just downloaded and install debian 7.3. In the early days of debian, they had testing, unstable and stable. What category is debian 7.3 in those three stages I mentioned?

My second question is why doesn't debian have firefox? I am using iceweasel which is from mozilla, but I still prefer firefox as to other browsers.

If you have the answers please let me know. Thanks

Stable. Iceweasel is Firefox. Renamed, for some reason. Performs just the same. Don't worry about it. :)

There's actually 4 versions of Debian:

oldstable (currently squeeze) - as the name implies, it's the last version of stable after a new version has been released.
stable (currently wheezy) - this is what you downloaded
testing (currently jessie) - The next version of Debian, will be fairly cutting edge until ~6 months before the release when it hits the freeze and will progressively get older and older in preperation for release.
unstable (always sid) - as the name implies, this is not recommended for any system where uptime and stability is important.

Firefox is renamed Iceweasel in Debian due to trademarks. While Firefox is fully open source, the name and icon are NOT open source, they are trademarks of the Mozilla coorporation. So Debian, who maintains that the "main" repository can only be FULLY FOSS, therefore cannot run Firefox named Firefox. But it's exactly the same software.

Thanks to both