For more background check out the wikipedia page.

Back story: Mozilla owns the Firefox trademark and wants to ensure that when the Firefox name is used the program is up to their standards.  This means that in order to use the trademark and logo, Ubuntu needs permission from Mozilla to distribute modified versions of Firefox.  Debian found that requirement too restrictive, and decided not to use the Firefox icon.  Debian created IceWeasel as the new branding for Firefox.

This reduces user familiarity with key software.  This made it less useful to recommend Debian desktop deployments.

Here is the kicker:

The Debian IceWeasel mascot is a Weasel humping the globe.

You can view a fuzzed out version here, but “If you install Iceweasel, you’ll be able to view the NON-MOSAIC HUMPING WEASEL!”  If you are running Debian and IceWeasel you can go the About page.  (If you really need to view it)

Congratulations to Debian for proving Mozilla’s point.  Mozilla does need to protect their trademarks and icons, if only to keep Debian from using an icon of a Fox humping a globe and distributing it as Firefox.

This is clearly unacceptable and to me indicates that maybe Debian should just accept the upstream Firefox branding. It would be better for all parties.