Understanding http requests

Add-ons Development
#1

If I have say 4 tabs. Normally, only one of them is active at a given time. For development purposes, I need to understand:

  1. Are HTTP requests sent or URL redirection happen in the inactive tabs?
    I am referring to the main address bar HTTP requests/URLs not the page contents.
#2

Yes, JS can still modify the location of a site even when it is in the background.