Firefox Desktop should be similar to Firefox portable. Note Firefox Desktop is now available in a 64bit version which may have advatanges as you mention you have 8GB of RAM

Fx50 will now be using a multi process mode in most installs, or at least most installs with no add-ons. Multi process should be much faster, but will inevitably use more CPU resources to give the increased speed. That renames plugincontainer as Firefox, and may run at least two instances of Firefox.

Not sure what you are testing when you say

Even with a new install without open tabs 
or any extensions installed, 
performance was dire for the same reasons as above.

How can you measure performance with no tabs open ?

Note enabling Firefox's Health Report

• Firefox Health Report - understand your browser performance

Will allow you to build up real data about your startup times. Also if you enable telemetry that shares data that engineers can look at

• Share data with Mozilla to help improve Firefox

See also

• Firefox uses too much memory or CPU resources - How to fix

Hi, John99

Thank you for responding and trying to help with this issue.

I have tried 64bit Firefox, didn't make a difference.

Perhaps the 2nd instance of Firefox appearing in Task Manager when opening the latest version is to do with multi-process, as you say.

What I meant by performance being dire when no tabs were open is, after installing Firefox, I opened it for the 1st time. So, more accurately, with only the start page open. By performance, I mean - fans ramping up, firefox using 25% CPU and upwards to 40%, other open windows of other apps become sluggish and responding poorly, firefox taking a long time to open and close.

Regarding the links you posted:

1st link - suggests using Firefox for 14 days to generate sufficient info to be usable, As Fireofx is currently unusable for me, this isn't an option.

2nd link - requires steps to be activated in 1st link.

3rd link - I have read through and tried all steps on a number of occasions without remedy.

The issues I'm experiencing don't happen with IE, Chrome, Pale Moon or Firefox Portable - just the desktop versions of Firefox for the last 7 or 8 versions, at least.

I even tried installing Firefox (version 47 or 48, I think) right after a fresh install of Windows 8.1, before installing other apps/programs, in case some other program was causing issues with Firefox. That didn't make a difference, either.

Huisie said

So, more accurately, with only the start page open.

What are you using as your start page?

Hi, FredMcD

The standard start page - what you get after installing Firefox and opening for the first time.

Yesterday, I downloaded the latest desktop version (it was 50.0.1), installed it and opened it.

- it took a while to open (and also to close)
- my fans ramped up significantly
- opening Windows Task Manager showed Firefox constantly hitting 25%+ CPU, up to about 40%
- every once in a while, it would dip down into the teens (10-20%) but then ramp up over 20% again.

I didn't install any extensions, I didn't open any web pages. The only page or tab open was the start/welcome page.

I did this process several times, opening Firefox and letting it run for several minutes, each time with the same result.

This time round, I didn't make any changes or attempt to tweak anything, such as deactivating plugins or hardware acceleration. I do not have Flash installed.

It seems odd to me, as noted by john99, that the desktop version should have issues while the portable version doesn't. I;m also puzzled as to why Pale Moon desktop version doesn't have the high CPU problem, either.

I have tried for months to figure this out (Google is your friend) but haven't the foggiest notion.

I am going to throw in the towel on this one, just stick to using the portable version.

Thanks to yourself and john99 for having a crack at this.

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac=Options) key, and then starting Firefox. A small dialog should appear. Click Start In Safe Mode (not Refresh).

Is the problem still there?

https://support.mozilla.org/en-US/kb/firefox-slow-how-make-it-faster

https://support.mozilla.org/en-US/kb/firefox-uses-too-many-cpu-resources-how-fix

https://support.mozilla.org/en-US/kb/firefox-hangs-or-not-responding

Firefox should not be a problem especially if Firefox Portable works. It could be a malware issue, it could be something odd in your profile or even corruption of the Firefox program files.

I suggest you try Firefox Developer Edition

• It installs by default as a separate browser with its own profile
• It has advanced troubleshooting & diagnostic features, most of which are enabled ready for use by default.
  • Listing of tools: https://developer.mozilla.org/docs/Tools (With links to tutorials)
• It is available as 32 & 64 bit versions. Go for the 64bit version to take advantagee of your 8GB ram
• The only disadvantage is it is for developers & testers and tends to update frequently, probably every day.

if you have no extensions and are not trying to load tabs and windows from previous sessions, or restore from a crash then I see no reason why Firefox should behave so badly. Must say if it does behave as described it is not going to be useable.

Hi, FredMcD I have tried Safe Mode, doesn't make a noticeable difference, I'm afraid.

Hi, John99 Thanks for the suggestion. I think I'm going to play around with the Developer Edition when time permits, see if I can get a read on what the problem is.

Thanks for your time, guys. Please consider my post closed. Don't mean to be rude, but work is hectic for next few weeks, won't be able to visit this with any regularity.

No problem. Hope you get Firefox sorted out and thanks for posting back.

Note we will be migrating to new forum software some time soon. You will need to reset you password when that happens, and I am not certain links to all older posts will survive the migration properly.