Restart firefox after you connect your screen--I've found on my linux laptop that connecting an external monitor with firefox open makes it freeze or be prohibi

Restart firefox after you connect your screen--I've found on my linux laptop that connecting an external monitor with firefox open makes it freeze or be prohibitively slow. You may have a different problem--but just in case. After doing that I've run it on my laptop's 4k screena nd a 4k external monitor on integrated graphics with no performance problems whatsoever.