https://support.mozilla.org/en-US/kb/update-firefox-latest-version 46.0.1

As a test, disable your protection programs.

FredMcD said

https://support.mozilla.org/en-US/kb/update-firefox-latest-version 46.0.1 As a test, disable your protection programs.

Fred - I have tried this (and again just now) and no joy. I'd agree this looks as if something is checking the page content, but manual diasbling does nto seem to work - why a full Safe Mode disabling deos I don't know. The task that goes to a high CPU % is the Firefox task, so it's either core Firefox or something such as a Plug-In which shows up as being Firefox task.

Just to be sure, you disabled Avast?

Type about:preferences#advanced<Enter> in the address bar. Under Advanced, Select General. Look for and turn off Use Hardware Acceleration.

Type about:addons<enter> in the address bar to open the Add-ons Manager. Hot key; <Control>(Mac=<Command>) <Shift> A)

On the left side of the page, select Appearance. Then select Default.

Now restart Firefox.

Hi Fred

Yes, definitely disabled Avast - both using the method above or by stopping Web Shield, or even the whole Avast, from Avast's shield controls. Hardware Acceleration was on, but stopping it did nothing. Appearance was already default.

One thing of interest (perhaps) was that afterwards (once - but I have seen it occasionally before) the page did actually load fairly quickly (1-2 secs) but the CPU and Firefox task go high for a minute or so. Note that if you close firefox when the CPU is high, the task does not terminate until after it has finished whatever it is doing and the CPU drops back to background.

I've attached two screen grabs - firstly the "normal" issue behaviour, then a second one where hl.co.uk loaded quickly (visually) but the CPU stayed high and Firefox task did not quit until 50 secs or so after I quit (X'd) Firefox. (each square on the graphs is 5 seconds)

I've called the big guys to help you. Good luck.

Start your Computer in safe mode with networking. Then start Firefox. Try Safe websites. Is the problem still there?

Starting The Computer In Safe Mode;
Free Online Encyclopedia

Will try the safe mode idea when I can.

In the meantime, I was contemplating moving to version 46 - and have found it looks unlikely to succeed since on another machine (and Linux Mint, not Windows) I have just updated from FF 28 to 46 and lo, the problem now occurs on that machine as well !

It confirms another behaviour - sometimes the page doesn't load visually until the high CPU ends, at other times, the page loads or part loads visually but the high CPU period still occurs and the page does not finish loading (the reload arrow has not appeared) (or follow a link on the page or load another page) until the high CPU period ends.

But again, starting FF in Safe Mode avoids the problem

Have reported at Bugzilla, though has not appeared in the database yet

It could be the work of one of your add-ons. Type about:addons<enter> in the address bar to open your Add-ons Manager. Hot key; <Control>(Mac=<Command>)<Shift> A)

In the Add-ons Manager, on the left, select Extensions. Disable a few add-ons, then Restart Firefox.

Some added toolbar and anti-virus add-ons are known to cause Firefox issues. Disable All of them.

If the problem continues, disable some more (restarting FF). Continue until the problem is gone. After, you know what group is causing the issue. Re-enable the last group ONE AT A TIME (restarting FF) until the problem returns.

Once you think you found the problem, disable that and re-enable all the others, then restart again. Let us know who the suspect is detective.

Fred

Thanks for the suggestions but I'm afraid I tried all that right at the start. That's the funny thing though, diasbling add-ons manually does not help but disabling them by starting FF in Safe Mode (Menu / ? / Restart with Add-ons Disabled) does work.

And it's not Avast since my Linux machine does not have Avast on it yet the new 46.0 install shows the problem.

Update - I also fully uninstalled the addons and that also makes no difference.

So, we therefore know that the problem is probably not the addons but somethign that is disabled / bypassed in FF's Safe Mode. Also, it's not Windows specific and is not gone in the latest Linux version of v 46

Type about:preferences#advanced<Enter> in the address bar. Under Advanced, Select General. Look for and turn off Use Hardware Acceleration.

Type about:addons<enter> in the address bar to open the Add-ons Manager. Hot key; <Control>(Mac=<Command>) <Shift> A)

On the left side of the page, select Appearance. Then select Default.

Now restart Firefox.

Did that. Didn't work.

Ah. There's an error in my logic as to whether starting FF in Safe Mode works to solve the problem - basically - this doesn't in fact work! The reason it looks like it works is that the problem only occurs on the first time hl.co.uk is loaded after startign a new instance of FF.

- If you start FF, then load hl.co.uk, wait to resolve the wait, then restart in Safe mode, load hl.co.uk, the problem apparently goes away. But in fact it doesn't as the page is still ?cached? and therefore loads OK as it's a second load, not because of Safe Mode, whereas....

- if you start FF, do not load hl.co.uk, restart in Safe Mode, then visit hl.co.uk, the problem is still there!

Doh.

Have submitted to bugzilla: 1272465

I've called the big guys to help you. Good luck.