I think it is completely non-silly. Debian was very simply and to the letter of the law in violation of the terms under which a piece of software can be called Firefox, and at any time Mozilla Corporation is entitled to bring civil action, as far as I can tell. My understanding is that at the time they were backpatching security fixes to derivative versions of Firefox -- specifically, older versions for which upstream had dropped support. What if one of those introduced an annoying crash or security problem? Is it fair that Mozilla Corporation's Good Name on the hook for it, if it does not wish to be?
If Mozilla Corporation (or would it be Foundation?) felt that they wanted to enable this kind of derivative distribution of their software, they could have very simply offered provisions like the Linux Trademark Institute: http://www.linuxfoundation.org/programs/legal/trademark. Clearly, Debian still has many references -- and modifications -- to Linux.
Problem solved. But, as far as I can tell, this was not to be.
I am not a Debian developer nor someone who was actively following that conversation, but when I heard about the decision I have not heard a single convincing (or even any) argument that it was an incorrect one, but again, I'm not familiar with the matter in great detail. Proprietary software companies can be awfully persnickety about...well, everything regarding their license and trademark, and I don't see why lack of adherence to a contract is acceptable just because there is Free Software (but not free trademark) involved.
The silliest part is the name chosen.