Opening Task Manager Slows PC to Crawl - Windows 10 Pro 1709

Same issue intermittently since Win10 Creators Update. Happens to my PC when Task Manager is open at the same time as a browser.

Chrome and Firefox are affected (... but not Edge?).  Task Manager stops responding. Mouse responses lag by several seconds. ditto keyboard. CPU and memory to spare as far as I can tell.

Only happens when browser is open. Disabling Chrome extensions and setting Chrome not to run extensions in background doesn't cure the problem. Problem doesn't arise with 3rd party Task Manager alternative (System Explorer).

If left open long enough in unresponsive state, Task Manager eventually starts responding, and mouse control returns. In my case, the issue then went away for a few weeks until today, when I had reason to reinstall Chrome from scratch. Now it's back.

Uninstalled Chrome and switched to existing Firefox browser. Same deal.

Tomorrow I'll try the wait and see approach with Firefox and report back.

My PC is Dell Inspiron, AMD Phenom II 2600 Mhz with 8 GB of RAM. Also runs Webroot AV.

Update - 2 hours later. Confirmed that issue is triggered by having Firefox and TM open at same time. All it takes is 2-3 clicks on TM (e.g. switching tab or from programme-name to CPU column) to cause TM to stop responding, then mouse/keyboard responses to lag until PC becomes uncontrollable.

Lag makes closing Firefox almost impossible but when I eventually succeeded in doing so, TM started responding again and HID control returned immediately. 

TM does not break PC when Edge is open.

For the time being I've disabled TM via the group policy editor and will use a 3rd party utility that doesn't conflict with Firefox/Chrome.

Webroot suggested I 'allow' Firefox under Identity Protection → Application Protection. I found four instances of Firefox in the list of applications, which I changed from 'Protect' to 'Allow'. After doing that, I can have FF and Task Manager open at the same time without losing control of mouse and keyboard input.

Earlier, I'd tried allowing taskmgr.exe in WR but that had no effect.

Other info: The TM problem initially affected Chrome as well, when Creators Update first installed. Current Chrome build isn't affected on my PC although there are many instances of Chrome in the Webroot app protection list, all set to 'Protect'.

Also, I've had an issue with WR Identity Protection before with another programme, WriteMonkey. Copy and paste stopped working after a WriteMonkey update. I eventually tracked down the cause to WR Identity Protection. Again, 'allowing' WriteMonkey cured the problem.

Yes! Excellent diagnosis! Task Manager freezes up when Firefox is open. I confirmed that I can use Task Manager fine when Firefox is closed. Has Mozilla been made aware of the issue?

It has been doing this ever since the Fall Creators Update.  I've tried all sorts of changes to Firefox's Performance options but nothing fixes it.  This weekend I set up a new quad core (Xeon) computer with 48 gb of RAM and a 1T SSD, and it was no better than on my worst machine.  And it's new, so nobody can blame some hidden corruption that's occurred over time.  I've seen this on every computer I own (several) and it's the same on all. I cannot believe that Firefox and Microsoft haven't addressed it yet.  Atrocious.

I've been having a similar problem for upwards of a year and I do not have Webroot installed. I use Google Chrome and Windows Defender. However, closing Chrome does not seem to fix the issue either.

Agreed! Hardware isn't an issue for me either. I am not using the machine in my original post, although that was no slouch. I am now on a Dell Precision T7600 with dual Xeon 6-core 2267 cpu's and 64GB of DDR3 1600mhz ECC ram. Still with my Samsung EVO 850 OS drive and a couple secondary drives.

Have you seen this issue posted anywhere other than here?  I can't imagine that they don't know about it, but wondering why it's not viewed as being important enough to fix it.