Trademark and logo issues
The name "Mozilla Firefox" is a registered trademark; along with the official Firefox logo, it may only be used under certain terms and conditions. Anyone may redistribute the official binaries in unmodified form and use the Firefox name and branding for such distribution, but restrictions are placed on distributions which modify the underlying source code.
To allow distributions of the code without using the official branding, the Firefox source code contains a "branding switch". This switch allows the code to be compiled without the official logo and name, for example to produce a derivative work unencumbered by restrictions on the Firefox trademark. In the unbranded compilation the trademarked logo and name are replaced with a freely distributable generic globe logo and the name of the release series from which the modified version was derived. The name "Deer Park" is used for derivatives of Firefox 1.5 and "Bon Echo" for derivatives of Firefox 2.0.
Outside of certain exceptions made for "community editions", distributing modified versions of Firefox under the "Firefox" name requires explicit approval from Mozilla for the changes made to the underlying code, and requires the use of all of the official branding. For example, it is not permissible to use the name "Firefox" without also using the official logo. The Debian project notably fell afoul of this, by using the name "Mozilla Firefox" but not the official logo, in a modified distribution (because of restrictions on its use, the Debian Free Software Guidelines did not permit Debian to use the logo). Although Debian claimed to have reached a prior agreement which would have allowed this, they were told in 2006 by a representative of the Mozilla Foundation that this was not acceptable, and asked to either comply with the published trademark guidelines or cease using the "Firefox" name in their distribution. Ultimately, Debian switched to branding their modified version of Firefox as Iceweasel.