It's not like they actually announced it. They wouldn't do something so suicidal. However, they have changed the code API that add-ons like adblockers use under the guise of "keeping people secure"

These changes have essentially neutered adblockers so they're only 10-20% as effective as they once were.

Firefox has gone out of their way to speak out against this, that it doesn't help privacy or security quite as much as they say and ensures their browser still includes the code required to make add-ons like adblockers work properly.

Firefox isn't the only option, but most other browsers are based on chrome. Meaning they don't have a lot of options. Some have opted to build their own adblockers directly into the browsers, howeever those adblockers aren't as good options as having an unaffiliated add-on that we can swap out if it gets dirty, and starts taking money from advertisers to deliberately stop blocking specific ads from them.

brave is a particularly bad offender. It specifically actually only blocks ads that don't come from its own ad service - using adblockers as a means to stop other ad services from competing with it.