3.6.8 a resource hog or another problem?

Question

Since recently installing 3.6.8 upgrade here - on an XP SP3 system which was previously performing efficiently - browsing has slowed to crippling speed. Open a more than a few tabs and my fans kick in like we're about to take off, and everything is grindingly slow and reluctant to respond. Even typing this, the letters appear in fits and starts, sometimes 4/5 words after I've finished typing them.
So, trying to diagnose things here, and FF seems to be a fairly suspicious potential culprit; often seen to be gobbling 90%+, regularly 97% and even 99% of CPU processes.
As a long term FF user, any suggestions gratefully received.

Answer 1

Issues of this sort are, unfortunately, more common and the we'd like them to be. However, they tend not to be cause by Firefox itself, but rather by software that is running either inside or alongside it, such as add-ons or firewalls. Since these issues have a broad span of possible causes, you need to diagnose your problems before fixing them. Follow these instructions ''to the line'', as they'll probably help you diagnose and fix the problems you're having.
#run Firefox in [http://support.mozilla.com/en-US/kb/Safe+Mode safe-mode] to disable all extensions, themes and plugins. If this fixes your problem, be it with RAM or CPU usage, then you know it's a problem with add-ons (plugins, themes or extensions). Proceed to number 2. If safe-mode doesn't fix your problem, then read bellow, after this list;
#update all extensions (go into ''Tools > Add-ons > Extensions > Find Updates''), themes and plugins (see [https://www.mozilla.com/en-US/plugincheck/ this page] in your Firefox. If this doesn't solve the issues, proceed to the following number;
#disable all extensions, themes and plugins in your Firefox (not running safe-mode). This is temporary and for diagnostic purposes only. Being certain that, as in safe-mode, the problems you're having have gone away, enable one plugin at a time. You should be certain that you actually want that plugin to be enabled. It's best to keep the overall number of enabled plugins as low as possible. When you encounter problems, you know you've found a problematic plugin, so disable it for good. Keep enabling all plugins (except problematic ones) until you've gone through them all. If you need support for a problematic plugin, you need to contact its author for support;
#enable one extension at a time. Again, be certain that you actually want that extension to be enabled. As with plguins, it's best to keep the overall number of enabled extensions as low as possible. Also, try the theme you want to have installed so see if that is what's causing the problem. When you encounter problems, you know you've found a problematic extension/theme, so disable it for good. Keep enabling all your extensions (except problematic ones) until you've gone through them all. Just the same as with plugins, if you need support for a problematic extension/plugin, you need to contact its author;
#if you've followed my instructions above, you're done! You've fixed your problems with problematic add-ons. If you want to keep using those problematic add-ons, please contant their authors for support.
Ok, now... ''If'' disabling all extensions and plugins through safe-mode didn't work to fix your problems (or, in other words, if you've just read number 1 on the list above and come straight here), then you have different issue. The most likely scenario is that you have a third party software running on your computer that is messing with Firefox. Detecting which program it is may be tricky, but the following list should help you. Make sure you follow it carefully. Don't forget to answer the question on the last point, if nothing else helps.
#try reinstalling Firefox. No data will be lost. You can get the latest version (for free, as always) at [http://www.getfirefox.com/ getfirefox.com]. Make sure you [http://support.mozilla.com/en-US/kb/Uninstalling+Firefox uninstall Firefox] prior to reinstalling it. For help installing Firefox, see [https://support.mozilla.com/en-US/kb/Installing+Firefox this support article]. If that doesn't fix the problem, proceed;
#do a virus/malware check on your computer. See [https://support.mozilla.com/en-US/kb/Is+my+Firefox+problem+a+result+of+malware?s=malware&as=s this support article] for help on this point. ''This is a very important step'', so please pay attention to it. If your problem is not due to viruses/malware, proceed;
#disable all software running in the background that you don't want to have running in the background (in Windows operating systems, this is done by pressing WINDOWS+R in your keyboard, typing ''msconfig'' and pressing Enter; now, under the ''Startup'' tab, you can uncheck the software you don't want, and reboot your system for changes to take effect; if you're unsure of what software you want running, ask someone with more experience). If this doesn't fix your issues with Firefox, proceed;
#check if your firewall/antivirus/security suite is conflicting in any way with Firefox's normal behavior. Check for enabled functions/features that you don't want and/or may be causing problems with Firefox. You'll find that these features are most likely tied to Internet Security features, such as link scanners or URL checkers and the like. If you're not sure they are conflicting with Firefox, simply try to disable them temporarily to see whether or not that's true. If this doesn't solve the issues, proceed to the following number;
#check your operating system security options, mainly advanced options that are not configured by default. While it's very unlikely that this may be the cause of the problem, it's remotely possible. If this doesn't work, proceed to the following point;
#update your modem/router software. There have been some reports that some modem/router software may cause Firefox and other browsers to loose performance and/or stability. If updating doesn't fix your issue, try other versions of the software, if possible. If you need support with this, contact your modem/router manufacturer. If this doesn't help, proceed;
#if you are using a Windows operating system, clean up your OS registry using appropriate software. There have been reports that badly maintained Windows Registries may case problems with Firefox. If this doesn't help, see the following point;
#please try creating a new temporary Firefox profile ([http://support.mozilla.com/en-US/kb/Managing+profiles managing profiles]) and see if the issues persist. Please report the results, so we can help you further.