Modern browsers have largely conquered the problem of popup windows
being created by obnoxious web sites. Nowadays the bad guys have moved
on to what is called "slide-in" or "fly-in" advertising. There you
are reading an article and some ad starts sliding in from the side
to nag you to subscribe to something or other.
I had been using the venerable Remove It Permanently
(RIP) add-on for many years but it was not up to the job of removing slide-ins. This add-on is my replacement for RIP. It uses the latest Firefox add-on technology to be much more aggressive in rooting out this stuff.
Note: This is the Web Extension version. See the Release Notes for the features that have been lost.