There are uBlock Origin filter lists to get rid of StackOverflow clones from web searches, such as:

* https://github.com/levymetal/filter-lists

(I don't remember where I took that one from, but probably was from this comment: https://news.ycombinator.com/item?id=33747333)

uBO already works fine on Chrome, Firefox desktop, and Firefox Android. Same syntax could be used to block any other domains, as desired. No need for a whole independent extension to just do that.