Iceweasel is Debian's fork of Mozilla Firefox. They forked it in
order to conform with their free
software guidelines, and to satisfy the Mozilla Foundation's
requests.
Now, when hearing that Debian had to fork Firefox because Firefox
wasn't satisfying their free
software guidelines, most people have to do a
double take at the very least, or will fire vitriol at Debian at
realising that they heard it right: Debian doesn't think that Firefox
is free enough, so they forked it. Debian demonstrates everything
that's wrong with free software zealotry; Debian needs to get off its
high horse; Debian is hurting all others who want to make free
software; Debian this, Debian that, blah, blah, blah. Then there's also the other extreme, zomg, Mozilla is teh evil; it won't allow completely free usage of its software; this is what happens when free software comes from defunct corporations; sell outs, blah, blah, blah.
In actuality, the drama is much less than that. What happens is that
Debian likes to tinker with its software, and often will modify
software that it nabs from around the world (the software from around
the world is called "the upstream source" in Debianspeak), fix it,
patch it, modify it, and often even send these modifications back
upstream. They did this with Mozilla Firefox, but Mozilla doesn't
accept modifications just like that. Now, since Firefox is after all
free software (it's also open source, but that's besides the point),
Debian is in its right to modify and distribute Firefox as it sees
fit. The one caveat is that although Firefox and its source itself is
free, its logo never was, although its name was until
recently, middle 2006.
What Mozilla used to request is that modified Firefoxes couldn't carry
the characteristic red-fox-humping-the-Earth logo and instead demanded
that an unhumped Earth without the fox be used as the logo. In
addition, modified Firefoxes had to be termed "community editions",
and this is exactly the path that the OpenBSD project has followed
with its Firefox: they modified it, removed the fox humping, and
labelled it Community Edition. Debian followed a similar path except
for not labelling it Community Edition, and Mozilla said this was fine
too, until recently.
Then in February of 2006, Mike Connor acting as representative of the
Mozilla Foundation told Debian that Mozilla no longer liked the way
Debian was using the Firefox software. They had two choices: either
use the official binaries provided by Mozilla, or remove any mention
of being Firefox from their software. Debian wasn't happy with the
Mozilla binaries because they contained bugs that Debian had already
fixed but that the Mozilla development team wouldn't adopt (they
wouldn't adopt them mostly because they referred to older versions of
the software and the Mozilla team works only on the latest version of
Firefox). Debian also likes to keep older versions of software
around for their stable distribution, hence the interest of patching
their own older versions of Firefox well after the Mozilla Foundation
has stopped supporting older versions. A further problem was that if
they kept the Mozilla binaries, then they couldn't modify them,
contrary to what is explictly expressed in Debian's Free Software
Guideline número tres:
Derived Works
The license must allow modifications and derived works, and must allow
them to be distributed under the same terms as the license of the
original software.
Thus Debian opted for choice number two: they removed all Firefox
branding from Firefox, renamed the term to Iceweasel
after a Matt Groening quote from Life in Hell, and they came up
with their own logo, a green blue network-looking sphere humped by a white
furry creature (presumably the aforementioned Iceweasel humping the
internet). Thus Debian gets to keep its own patches and security
fixes, and at the same time Mozilla gets to keep its brand recognition
without interference from Debian. Thunderbird and Seamonkey had to undergo similar treatment and became Icedove and Iceape respectively.
Iceweasel is based on version 2.0.* of Firefox, and save for the name
and who humps whom, it is identical to Firefox as far as I can tell
down to the very same legendary memory leak that has been unfixed for
years in Firefox (although I understand that there are minor fixes
under the hood).
There are still a few traces of Firefoxness branding here and there,
such as the page from The Book of Mozilla still hasn't changed
(perhaps, "And Lo, The Father saith, thou shalt not fly in my name,
whence the heat grew cold and still the followers of Mammon trembled
as Fire and Ice together may crush their souls" would be a suitable
replacement?), and here and there a few other files still have the
Firefox name in them, although presumably those will also be
eventually removed.
So it's not a big deal, and Debianistas aren't all a bunch of
religious zealot nuts (except perhaps for myself), they are simply
adhering to free software principles and playing friendly with the
Mozilla Foundation who is asking its brand to be respected, and Mozilla isn't a heartless baby-eating company just because they are requesting brand name recognition. As for the
rest of us, we still get our software, and we can still use it for
whatever purpose and poke around its internals if we so feel like it.