Paul posted:

but tabs within a browser have foreground and background.

Thank you for the clarification words that "focus" is the Windows thing
where the mouse and keyboard act currently.

This is about "foreground" and "background" of a given browser window.

There's one more complexity that Hathie brought up which I didn't consider
at first which is that we can start a browser and open the two tabs, one
pointed to speedtest and the other blank and then we can break them apart.

I followed Hathie's suggestion and broke those two tabs into two separate
"windows" which I made so small that they fit on the one screen with no
overlap where each now separated tab could be in the foreground
simultaneously I think

With three Windows open (one being this edit) I was able to cycle the
Windows "focus" between the three "windows" where the speedtest worked
without stopping.

I then overlapped all three windows and tried again and it still worked.
That means the focus doesn't matter as you were telling me.

The browser "window" just has to be in the foreground state.
It seems by "definition" any single-tab browser "is" in foreground state.
It's only with multi-tab browser windows where background exists.

What I want is to just trick a multi tab browser into thinking it is
foreground on all the tabs. That might be impossible or maybe not since
those annoying videos play even when the browser isn't the foreground tab
when I open a dozen google news links.

I'm always hunting for the one browser tab that was in background but which
still played the annoying news video or advertisement.

Even without being able to put all the browser tabs of a multi tab session
into foreground mode, the workaround by Hathie works which is to separate
the individual tabs into single tab browser windows which are by definition
in foreground mode.