Mitigating Browser Throttling:

Firefox: (After version 58)
  1. Go to [about:config] in the browser address bar
  2. search for "dom.timeout.enable_budget_timer_throttling"
  3. set value to false
Chrome:
  1. Go to [chrome://flags] in the browser address bar
  2. Search for "Calculate window occlusion on Windows" and set value to disabled
  3. (Optional on newer browsers) Search for "Enable occlusion of web contents" and set value to disabled
Edge:
  1. Go to [edge://flags] in the browser address bar
  2. Search for "Calculate window occlusion on Windows" and set value to disabled
  3. (Optional on newer browsers) Search for "Enable occlusion of web contents" and set value to disabled