1. Mozilla is working on that through the Electrolysis project,
https://wiki.mozilla.org/Electrolysis

2. ... identify rogue sites in Firefox
How would you define a "rogue site"?
Firefox running on a 900MHz processor with 500Mb of RAM might be slowed to a crawl by a Flash or Java presentation, while a 3.0 MHz multi-core processor running 2 Gb of RAM probably wouldn't skip a beat. Sure a "timer" could be added to Firefox to alert the user a the problem caused by web page plugin content, but that would probably just piss-off users like the JavaScript "timer" alert does now, by them having to respond to repeated alerts. I doubt if anything like that is going to be added to Firefox.
Have you seen the FireBug extension?
http://getfirebug.com/
You might be able to use it to identify problematic websites, but as far as running it all the time - it can create its' own problems. Plus, some of the FireBug features are going to be built into Firefox 4 - Web Console.
https://developer.mozilla.org/en/Using_the_Web_Console

There are a few ways to limit what runs automatically in Firefox, as far as plugins goes. Flashblock, but that only controls Flash. Or NoScript, which can block most plugins from automatically loading content; it provides a button that you can click to run each presentation ala carte as you wish.
I use NoScript on my EeePC (Ubuntu 10.4) to stop plugins from automatically running content, especially in Tabs I just opened and not looking at. I rarely hear the CPU cooling fan kick in since I have been using NoScript - just to control the plugins, I'm not using it to block JavaScript.

Thanks for the reply, very useful. I take your point about a slower PC but this makes it easier to identify badly written code. If every developer had a slow PC they would write more efficient code.

I use flashblock, however, on some sites they still slow down the PC to a crawl.

I do not want a bug reporter, but if nothing else something that when activated added a percentage of each firefox tab in CPU, memory and network resources would be very helpful.

I agree with zappo, I do need to work on machines on which the configuration is less than optimal, yet I may need to access drivers, specifications, and setup programs without been driven insane by unruly scripts.

I don't think it is reasonable to merely say that one must be more careful whilst browsing. I don't think I should have to install, then uninstall a tool like NoScript just to complete my job.

I believe it is reasonable to ask for Firefox to have some embedded code that detects which tab is causing a machine to slow down due to excess resource utilization.

I agree on the simple availability of cpu (and maybe memory) per tab. In work scenarios where I have to use IE I can use ProcessExplorer and pretty well narrow down a culprit eating high CPU time. With FF under ProcessExplorer it shows as one item. I already use selective script blocking and selective flash blocking but still sometimes find something eating a ton of CPU and the only solution is to close FF and reopen them all and often the problem is cured. Just knowing which sites tend to eat more than typical CPU usage would be good to know.

I'm with Zappo. This has driven me nutz for a long time. I mostly always run Firefox with many tabs - now 36 ! I'm writing this from Chrome - as FF is running too slow. One or more tabs has some script running that is chewing up excessive cycles on my older Pentium 4 4GB system. Damned if I know which one ! All running programs are turned to slugs. The only solution is to close 'em all & reopen only one tab & start over building the key tabs I'm interested in from the tab history. There has to be some way to identify runaway tabs. C'mon you Firefox geniii - pls !

I usually work with many simultaneous opened tabs (36 at this moment).

I followed The Edmeister suggestion by installing the NoScript addon and tried it for a while.

In my opinion, using NoScript as a way of identifying ONE offensive tab (or plugin) among MANY, MANY opened tabs is not practical at all!! (specially when comparing to Chrome Task Manager, which is really straightforward)

I'm not complaining about NoScript: actually, it seems to be a rather powerful tool in terms of security issues, fully customizable, etc, etc, for those who need it.

But it's not my case.

The point is that if it was not because of this high CPU usage caused by ONE tab (or ONE plugin) among many others, I wouldn't be using NoScript, since I don't have any security needs.

I've been using Firefox as my only and unique browser until today, when I decided to switch to Chrome due to this issue.

I'm glad to read that Firefox team is tackling this issue in the Electrolysis project.

But, until it finishes, I will be using Chrome (against my will).

I subscribed this post so that, I assume, I will be notified when the issue is solved.

Note: In case you developers need to know, either during development or test, what I noted in comparing Firefox performance against Chrome, both with around 35 simultaneous opened tabs:

1 - I was getting around 50-60 CPU usage with Firefox, be it active or minimized; 2 - With the same tabs opened, Chrome seems to act as follows:

 2.1 - When browser is active and a heavy tab is active, Chrome also gives high CPU consumption;
 2.2 - If I select another tab, one that is lightweight, then Chrome automatically reduces CPU consumption, as if it turned all other tabs inactive;
 2.3 - If I minimize Chrome, even when the last active tab was a high CPU consumption one, then Chrome reduces CPU consumption to around 20%

3 - In my case, I noticed thru Chrome task manager that what was causing high CPU consumption was a Shockwave Flash object. That object shows at Chrome task manager as a separate line as if it was another tab. Actually, when I dropped it, I noticed that all the tabs using Shockwave had it dropped at once, although the pages themselves remained the same (except the frames within them using Shockwave). I think that showing objects as Shockwave like Chrome task manager does, separate from tabs, makes it very easy to identify CPU offenders. But, like I said before, when minimizing Chrome, all tab activity seemed to be stalled, giving the above mentioned overall CPU consumption of around 20%.

Thanks to all.

I agree. I'm running Firefox 12.0 on a 1.5y old 10.6.8 MacBookPro with 8GB RAM, using FlashBlock and AdBlock and only visiting reputable "safe" sites. (Altho, HuffPost may not be "safe" as it seems to chew up the CPU cycles.) I still get the CPU problem. Particularly annoying is CPU use when FF is minimized. If FF is minimized, it should use _minimal_ CPU, to my mind in any case; but even when minimized, "Firefox Plugin Process Shockwave Flash" still plugs along, gobbling a steady 20% CPU. The real offender is Adobe and their Flash monstrosity, of course, but FF should have the fine tune controls to rein in a particular tab when it tries to hog resources.