Since the last upgrade Firefox regularly crashes. It becomes very slow then none of my tabs I may have open will load. Task manager tells me I have up to 27 firefox items running sometimes using huge amounts of CPU
Have you tried to restart the computer and trying the Browser again? And did you also try Firefox Private Mode Browser to verify Addon or something is causing the crashes?
The number of processes seems not unusually large. The article linked below relating to CPU and memory usage may help. To get support for crashes, see the second article.
Yes I have to restart everything now and again which works for a while. If I have loads of Firefox processes open, usually just one of them seems to be using an enormous amount of CPU the others none. I have closed the active one and everything works again. It would be useful if we could understand which process is doing what but they are all just labelled Firefox. Why do we need so many anyway. I've just been through my open apps in Task Manager and only one item had two apps running. Yet Firefox has 29 at the moment. (I have 10 tabs open if that makes a difference)
Memory and cpu usage depends on the sites you have open. If there are any you are not using, you might consider using this extension to unload them.
These may help explain the number of processes.
You can check the about:memory and about:processes pages for info about all processes. There are several toolkit.aboutProcesses prefs on the about:config page to show more info. See also the about:unloads page for info about the tabs.