It will break my heart, but must I abandon Firefox?

Question

UPDATE 9th Feb <br />Issue now SOLVED in the other thread.<br /> Disabling McAfee SiteAdvisor resolves the issue in this instance. [/questions/984055?page=2#answer-532036] <br />Note presence of ''McAfee MSS+ NPAPI Plugin''
Please see and continue with thread [/questions/984055] ~J99 Modified February 1, 2014 9:39:33 PM BST by John99
Almost two weeks ago, after years of admirably flawless performance, my Firefox 26.0 was struck by recurrent episodes of complete unresponsiveness, and frequent crashes.
Efforts to remedy these problems, involving disabling various add-ons and JS, failed.
Now I have some important new information. When operating normally, Firefox never uses more than about 3% or, rarely 5% of my CPU, even when I have many tabs open to websites, even when several of those websites are playing videos, etc. (I have had the Task Manager open constantly this week in order to be able to close Firefox when it's so unresponsive I can't use X to close it, so I was in a position to observe CPU usage.) But when Firefox is in the early stages of an episode of unresponsiveness (for example, when I can't download files or play videos) the CPU usage is greater than 25%. What's even more remarkable is that if I then close all tabs, and have only one “New Tab” open (so that I'm theoretically not using Firefox at all), the CPU usage remains over 25%!!
Over the past few days I've a) confirmed and reconfirmed this perfect correlation between Firefox's unresponsiveness and a dramatic, unprecedented increase in CPU usage to in excess of 25%, occurring completely out of the blue, in no way triggered by my doing anything, and b) verified that when Firefox is responding normally, NOTHING I do causes the usage to go above about 5%.
But the question is: what is causing this abnormal CPU usage that is clearly associated with Firefox's unresponsiveness?
For the record, I have run repeated scans using Windows Defender and MalwareBytes and nothing malicious has been detected, and I have had no other problems with my computer besides the ones with Firefox. Chrome continues to operate perfectly normally.

Answer 1

I suggest you continue this conversation in the thread you have already opened.
The fact that you are using the CPU heavily compared with normal may help explain the Firefox unresponsiveness.
The question is what is it doing.
*Is it a direct Firefox process taking up this CPU use.
** If so why. <br />is malware running and making use of Firefox ?<br />Is this only on close down ?<br >is it only on a particular site ?
*Is it the plugincontgainer ?
*Is it another process that may affect or slowdown Firefox ?
** can you identify the process.
** is security software involved, scanning or updating
Presumably sysinternals software - now available from microsoft - will help you answer such questions.
Ensure you give the information in the other thread so it may be considered along with the details you have already posted.
*''' The thread is ''After years of happily using Firefox, sudden, recurrent calamity'' [/questions/984055]'''
Back to basics
You really need to troubleshoot by using Firefox
*in a new clean profile
* with all plugins disabled
*in Firefox's safemode
*even try it with only this forum open as the only tab
I would hope in such a configuration you do not get
* 25% CPU usage.
* Crashes
We should be able to work from that to figure out what else is implicated in your problems.
Please answer in the other thread [/questions/984055] .