Does anyone have this issue were firefox becomes slow if left open for a long time. In my case after a couple of weeks rendering becomes slow and when I use youtube for example if is laggy, just trying to change volume taka few second to show the volume bar. It also happens to my laptop at work. I have around 30 tabs open.
You can see the worst offenders in firefox by using the hamburger menu then more tools and Task manager. You can sort by ram. YouTube likes to hold gigs of ram for some videos. Close the biggest offenders and you’ll get back close to normal speed.
Ding ding ding, the only good reply in this thread.
The symptoms described by OP smell like good old memory exhaustion.