The reason I first used it was they had a way to bypass the limited list of extensions that Mozilla allowed to be installed but this is no longer an issue so no real idea what the benefit is anymore. I’d guess at disabled telemetry but don’t quote me on that.

I switched to Ironfox a while back but still keep fennec around for the occasional site that Ironfox breaks.

I’d guess it would be the owner of the billboard advertising the space. I’ve definitely seen that before, often accompanied by a “x thousand people see this every day!” type message.