For some things like speedtests and video downloads, the web servers stop
working if you don't keep "their tab" in "focus" (I think that's the word
to use).

An example is speedtest.comcast.net which doesn't like when you focus on
something else while it's running. Luckily it doesn't take long but plenty
of other things do.

Is there a way to trick a browser tab into THINKING it's in focus?