High CPU & Memory issues - Excessive and unnecessary CPU usage in Firefox for Windows (see also questions1003966 & 998289)

Question

I am using the latest version of Firefox, 32.0.1, on an HP Pavilion dv7-4141sa laptop computer, running Windows 8.1 Pro 64-bit. There should be more than enough power here to run a browser without any problem, yet the computer is regularly being overloaded by the browser's resource usage.
I am currently measuring typical average CPU usage of 45% - with the browser minimised. That is to say, Firefox is not doing any browser jobs - it is not drawing on the screen - but it is using the most CPU of any process currently running. Why?
I am an ex-software engineer, and my understanding of current application development technology is limited, but I think I can say with some confidence that many techniques and software architectures exist that enable the suspension of program activity, or at least its reduction to a very low bare minimum, when the program is not actually carrying out its design function, which is in this case to draw pictures of website data on a screen.
There is a very serious problem here, one which means that I cannot run Firefox all the time, but have to kill it when I am not actively browsing, otherwise other applications cannot run to their full capacity. This is a great pity, because I have committed a lot of effort to making Firefox my primary web tool. It manages all my many bookmarks, contains my secure password manager (LastPass), manages my web security (via NoScript, AdBlock, and FlashBlock), just for a start.
Before any well-meaning moderators or other commenters start down the usual trail of "have you done this, tried that, disabled the other", I should point out that I have followed all the advice I can find, with no positive outcome. This computer is running a fresh installation of Windows, and a fresh installation of Firefox. At the moment I am running a new test Firefox profile.
The latest version of Adobe Flash, 14.0.0.179, is installed but disabled. When it is enabled and in use, Firefox's CPU usage seems high over longer periods, but overall there is little difference. It doesn't look as though the problem can be laid at Flash's door. A few other add-ins are installed, mainly those mentioned above, and Firefox is skinned with LavaFox v2-Green, but I have previously started from a clean installation, which has made little difference after an initial period during which things seemed to be better. Turning off or disabling various add-ons has made no discernible difference.
Just now I turned Flash on, and after a long period with Firefox minimised, Resource Monitor reported Firefox at 8% average CPU and FlashPlayerPlugin at 0.32%. While running a small video, RM reports FlashPlayerPlugin at about 45% and Firefox at 8%. After the video, Flash went back down to around 0.4%, and after a bit more browsing Firefox went to around 17% minimised. There seems little rhyme or reason here, except that Flash does not seem to be the culprit, although Firefox does seem to consume less when fewer tabs are actually active, as you might expect. I just refreshed more than a dozen tabs, and now Firefox is at 30%, but still not back up to the higher figures. Weird.
The CPU usage does vary a lot around the average, but 30% is still a lot for a program that shouldn't be doing anything above the minimum status maintenance, and still puts it at the top of my Top Process Monitor list. (Right now it's gone back up to 45%, without my using it in any way).
I have Telemetry turned on, so presumably Mozilla is recording some of the relevant data.
This is a very serious fault, which is more or less reproducible and which a lot of people seem to be experiencing. Probably more people have it than realise, because most users will not know anything other than that their computer slows down for some non-obvious reason; they may just think it's something to do with the computer itself, not knowing how to use the Resource Monitor and interpret the results.
Oddly, the problem does not seem to occur when running Firefox under Linux Mint 17, where the response is snappy and the CPU usage ostensibly low; I am going to look at this in more detail shortly.
I am not posting here for advice, but for information and as a form of bug report which hopefully other users will see. It will hopefully spare them a lot of effort and time in trying a lot of recommended "solutions" which will not work. The problem is inherent in the software, and can be solved only by Mozilla.
I am willing to supply any diagnostic data requested; as I said above, I have also turned on "Telemetry". However, I will not be trying out any more reinstallation/new-profile/add-on disable-enable-delete cycles unless I am asked to for very specific reasons. Please do not suggest courses of action which have already been mentioned elsewhere on this forum. I have tried them all.
The situation is very disappointing, but I have confidence that the Firefox developers will pin down the fault eventually and engineer a satisfactory solution that makes it viable to leave Firefox open all the time. Even with that restriction, it's still far better than the alternatives.

Answer 1

I share jmward's frustration. This is not a bug report so much as a request for a badly needed feature, ie the ability to have Firefox be able to tell us which tabs on which windows are eating time so we can target them. There are some very poorly written web pages out there which just plain loop while making no updates or inconsequential updates on the page.
This is not a OS problem; jmward runs Windows and I run Linux but we have the same issue. It is not a question of Firefox plugins or extensions, or even viruses; I have a new, clean Linux install but have the same problem on both my regular Firefox AND on a FRESH install of the latest Firefox (35.0.1) which has *NO* non-default plugins or extensions.
Here is an example of a web page which will eat 100% of one CPU's time:
http://patch.com/massachusetts/arlington/arlington-woman-allegedly-attacks-neighbor-snow-blower-0
I will attach 3 images to back up my claim. All of the images show my dark blue system monitor (gkrellm) superimposed on the web page. The top graph shows CPU time. I have 4 CPUs in my machine, so 25% means the web page is eating 100% of one CPU equivalent.
The first image shows the load of the offending page with elevated CPU usage along with the download net activity on eth0, but the CPU activity does not stop when the download activity is over.
The second images show the steady state 100% CPU equivalent of this page just sitting there apparently doing nothing. It IS, however, doing at least two different things. I know from my regular Firefox where I have "Remove It Permanently" installed that if I remove the the little weather indicator in the upper right of the offending page that CPU utilization drops to about 40% of one CPU equivalent. If I use RIP to remove everything else right down to a bare screen that 40% utilization stays until I delete the tab.
The third image shows the CPU utilization drop to zero when I delete the tab holding the offending page.
Now I will add a note here: If the offending page is NOT the top tab in a window then it stops eating time. The offender will also stop eating time if I minimize the window. However if I have another window up but leave the offender up on top in its window it continues to eat time even tho I am looking at another window. The offender will continue to eat time even if its window is completely covered by another window, and it will also eat time if I switch to another desktop.
I will often have half a dozen windows open, and there are many pages out there which will suck endless CPU time. Unless I want to open up a new tab on each window before I leave it there is likely to be some tab on top eating time uselessly. Get a couple of those going and Firefox becomes sluggish and can even stop responding for many seconds.
I guess I not only want to have Firefox tell us which tabs are eating time, but I would also like it if Firefox would stop giving CPU time to any tab which is not visible because it is covered by some other window and/or it is on a desktop which is currently not showing. If you can stop a tab's CPU usage by reason of tab-not-showing then you should also be able to stop its CPU usage when the window is covered or on the not-top desktop. Indeed is there any reason to not schedule absolute CPU utilization priority to the visible tab on the window with focus and give time to the other tabs only when the visible tab isn't using time?
My final thought on this is that I have had Firefox SO tied up sometimes that I swear their are web pages which are eating time even tho they are not the top tab. I regret that I do not have an example to show you. But Firefox grinds to a complete halt on a regular basis, and that is not acceptable. I am a programmer with long experience in multi-threaded programs so I *know* there is no reason you cannot do better. If there were another browser around which had the commitment to privacy which Firefox has I would probably switch out of shear annoyance. :-(