And practically speaking, the back-stop is that if uBlock Origin causes too many high-profile websites to break, it'll get a reputation for degrading user experience and fewer users will install it.

When two independently-owned systems on the web break each other, "who needs to fix their stuff" is a question more of social networks and business politics than technology. TeeSpring's "fix" could be to pop a banner that says "WARNING: uBlock Origin breaks this site and we can't test for that."