Yep, trademark law is different from other types of IP - unless you can show you've continually defended a trademark, you can lose the rights to it. However it's not always handled the same way:
- Red Hat asked people to rename unofficial RHL distributions something like Pink Tie back in the day, and the tradition continued with CentOS and the like.
- Firefox has a different tack, and just makes sure people sign up to meet certain specs to be able to use the trademark. That might mean not diverting from upstream too much (eg, Debian wanted FF to use Linux FHS standard, FF upstream didn't do that, hence Iceweasel).
Iceweasel is called like it is called because (roughly):
* The firefox branding itself is non-free, which is unacceptable for debian
* The replaced the branding, but kept the name first
* Mozilla complained and clarified that a program called "Firefox" has to bear the official logo
- Red Hat asked people to rename unofficial RHL distributions something like Pink Tie back in the day, and the tradition continued with CentOS and the like.
- Firefox has a different tack, and just makes sure people sign up to meet certain specs to be able to use the trademark. That might mean not diverting from upstream too much (eg, Debian wanted FF to use Linux FHS standard, FF upstream didn't do that, hence Iceweasel).
Not a lawyer etc.