Stable Version

Anthony "Tor is infamous for doing this with Firefox (Mozilla' being fine with it) as they simply took Firefox ESP and replaced the name Firefox with the the Tor name over it and declared it "The Tor Browser" when it's nothing more than Firefox ESP. Most people using Tor don't know they're using Firefox ESP lol."

I don't use Tor or have any interest in the Tor browser, but I think something needs to be said:  The Tor browser is an independent browser based on Mozilla's https://www.mozilla.org/en-US/firefox/organizations/.  It is not Firefox ESR with the name changed and that alone.

The Tor Project takes Firefox ESR code and changes/adds patches to the base code to (a) enhance anonymity, (b) enhance privacy and security in a number of ways, (c) in most recent iterations, embed various Tor extensions directly into the modified browser.  The Tor browser also changes a number of Firefox preferences from the default configuration.  The details are readily available in Tor Project documentation about the browser if you are interested in the details.

What Tor is doing (developing a specialized branch/fork of existing open source code to meet specific needs) is common in the world of open source software (the branching and forking from Star Office to OpenOffice.org, then to Apache OpenOffice and LibreOffice is a good example), and (in general, with limitations) freely permitted under https://www.toptal.com/open-source/developers-guide-to-open-source-licenses so long as the branched/forked code remains open source rather than proprietary.   

The Tor browser branch/fork of Firefox ESR is not at all similar to the situations you describe.