I'm aware that Mozilla Addons require a license and I also do know that the Addons webpage does list the license, although in tiny letters on the side, showing no emphasis on freedom. Do note that this not the case for the in-browser addon search (Tools -> Addons -> Get Addons), which hides this information as far as I can see. Moreover, there's no way to do search only in the subset of addons that are free as in speech, in neither interfaces. Free and non-free software are equivalent in there and users will just pick what looks fancier, without anyone ever educating them about their freedoms.
You are right that I should file bug reports, however I do think that this is not an error in passing but rather a deliberate choice on Mozilla's side. Sticking to your principles has a cost and makes you less popular to average joe who doesn't care about such things (at least that's what he thinks). That's not entirely guesswork: I've pointed out the addons issues above to a Mozilla person before (granted, not *the* person responsible for it) and I was basically told "meh, wontfix". But yes, this probabl belongs on a bug tracker, you're absolutely right.
As for "it's HTML5, just do View Source", please get *your* facts straight. If there's no clear copyright license, or the copyright license is not a free software license, it's a copyright violation to even study the code (modulo rights to reverse engineer that exist in many countries), let alone modify it for your needs and redistribute it. I hope you're not suggesting to take e.g. the Twitter "app" and derive an identi.ca one from it :)
It might be unfair to judge Mozilla for the lack of free software advocacy. However, as Mozilla is moving more from just being a software author and to the software distributor realm, I think we have to adhere it to Linux distros standards and criticize them for not having a clear stance on that.
As for the "open web" vs. FL/OSS, I think moves such as the Marketplace one are problematic to me, a free software zealot. Also see my previous LWN comment on B2G: http://lwn.net/Articles/484552/
(Gerv's response made me feel slightly better; I'm cautiously optimistic, but moves such as the Marketplace don't make feel any better)