When we see that something does not work perfectly on our PC, or that is what I do because I am used to good performance and speed, we look at what is happening on the system monitor. From it we can see what is occupying the RAM, CPU and other parameters, and from the application itself we can force its closure or kill the process. If the only thing that fails us is the browser, we can look at the Task Manager like the one that includes Firefox.
The first thing I do if I notice something strange is to look at the app system monitor to know what consumes the resources and, if Firefox is loading my session, then I would already enter the browser's Task Manager. To access it we have two options: the first is write in url bar about: performance (about performance); the second is to go to the hamburger (options) / More / Task manager.
Task manager to find out which Firefox pages or extensions weigh more
Once inside, what we will see will be something like what you have in the screenshot that heads this article: all the open tabs and the extensions that we have installed. On the assumption that my Firefox was bad, which was not the case, the culprit would have been the WordPress editor of LinuxAdictos, since it is not one of the lightest pages in the world. On the other hand, the control panel of the same blog does not consume even a fifth of what the editor consumes. So, in this case and if my team suffered, I would have to avoid opening multiple tabs with the WordPress editor. Or, if Firefox is almost hung, try close an editor by clicking on that option and then on the X that appears on the right.
If we have several pages open from the same site, they will appear on the same line and we will have to expand it by clicking the little arrow that appears on the left.
The Firefox Task Manager can also help us to know if an extension is what is making our lives impossible. In the screenshot that I have added, none consumes practically nothing, but I know that many users install many more than I do and one could put you in a bind. The Task Manager will tell us which extension is being revealed.
I think it is a tool that can be very useful and personally I would make it more visible, but good. Exists.