Iceweasel actually modified Firefox, this sounds more like bundling Firefox with other stuff in the same installer package. Vaguely reminiscent of distributing a Linux ISO that installs Firefox, along with other stuff...
Except that the Linux ISO is not called "Firefox." It would be OK for the Linux distribution to use the Firefox trademark descriptively to say that it includes Firefox, but that's not what these adware vendors are doing. They're calling their "Firefox bundled with some adware" Firefox.