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.
What you’re describing is called a resource leak. Something, an extension, a background process, etc., is holding onto resources for too long without cleaning itself up automatically.
This is pretty common in writing code, and extremely difficult to prevent except in closed and well understood systems. A browser is anything but that, due to the nature of needing to work on any website doing whatever they want.