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.
Check the RAM usage of each tab. My Firefox is constantly open at work, albeit with anywhere from 1-10 tabs, and it never gets slow. Only time I restart it is when Firefox updates.