Iceweasel was a re-branding of Firefox introduced by Debian because of license issue. The issue was solved in 2016, as explained in this bug report renaming Iceweasel to Firefox:
As PhilGil wrote on the Debian Forum :
"I'll miss Iceweasel too, but eliminating the rebranding will free up the Mozilla team for more important work and maybe allow them to push out updates in a more timely manner."A far more detailed article: The end of the Iceweasel Age.
"In essence, then, the logo-licensing problem, the trademark-usage incompatibility, and the patch-maintenance problem have all been resolved, so, Ledru said, Debian could return to the Firefox branding."Note the patch maintenance problem was solved thanks to the Firefox ESR (Extended Support Release).