Sorry, mistake above. I should have said, "I have tried Refresh, and also checking that various things like proxy, IPv6, accessibility etc that are mentioned in the forum (which I am having to access through Chrome, of course) *are disabled*"

Answering my own question... I recalled that I had set up some kind of integration with Xbox, for a specific purpose that was no longer required (and didn't work out anyway). So I uninstalled the Xbox app... and after the next reboot of the computer, everything was back to normal. I hope this might help others.

Aaagh! I spoke too soon. It's back - can't do anything. I notice that the revision number is 58.0.2 - is it going to do this to me every time a revision comes out?

Try to disable accessibility services in Firefox.

• Options/Preferences -> Privacy & Security -> Prevent accessibility services from accessing your browser
• https://support.mozilla.org/en-US/kb/accessibility-services
• http://techdows.com/2017/08/firefox-57-prevent-accessibility-services-accessing-browser.html

Thank you for the suggestion. However, I already have Accessibility Services disabled. And Firefox is still running ridiculously slowly - though not quite as slowly as it was when I first had 58.0.1. But I can load up Chrome, do the job I am interested, and close it down, in less time than it is taking Firefox to get itself open and displaying a page. And Firefox won't even close down properly - I usually end up loading Task Manager to force it down.

Did you try to disable hardware acceleration and check for issues with multi-process?

• https://support.mozilla.org/en-US/kb/performance-settings

You can try to modify multi-process settings to see if this has effect.

• set number of content processes to 1 if it is currently set to a higher value (4)
  Options/Preferences -> General -> Performance
  remove checkmark: [ ] "Use recommended performance settings"
• disable multi-process windows in Firefox

You can disable multi-process windows in Firefox 58+ by setting this pref to false on the about:config page.

• browser.tabs.remote.autostart = false

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• http://kb.mozillazine.org/about:config

• http://www.ghacks.net/2016/07/22/multi-process-firefox/

cor-el, thanks for your further suggestions. Unfortunately neither disabling hardware acceleration, nor reducing the number of content processes to 1, nor disabling multi-process windows has any effect. It is still proceeding at a snail's pace - and not a well-nourished snail's, either.

You can create a new profile to test if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Thank you, cor-el, for your continued efforts to help. I have tried creating a new profile, but it does not resolve the problem; if anything it makes it worse, which suggests that some of the tweaks I have tried hitherto were helping a little. The problem exists only on my desktop, not on my laptop running on the same network. There's nothing I'm aware of that's odd about the machine; it has an old spare hard disk installed to take the Windows automatic backups, and it's attached to a file-server as its main data store, but I can't think of any reason why either of those should interfere with Firefox.

I just gave up on this and switched to Chrome; I did try a complete reinstall of Firefox, but that didn't solve the problem. But today I absent-mindedly opened Firefox, and, presto! It is working properly again. In the interim it has updated itself to version 59.0 (64-bit), and maybe that has cured the issue.

And then I went away for a few weeks. And when I came home, Firefox updated the first time I ran it, to version 59.0.2 - and now it won't work again. Same symptoms - ridiculously slow, won't even close itself down. What is it that the updaters keep doing, or forgetting to do, that is poisoning it for me? So, back to Chrome.

HI, uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files , C:\Program Files(x86) & C:\ProgramData Then restart system. Then run Windows Disk Cleanup. (Note: This should be Pinned and run Weekly, If never done below expect 10's of gig's) Then run it again and click the button that says Cleanup System Files. Note: your Firefox Profile is saved. But you should make a back up before you do :

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Reinstall with Current Release Firefox 59.0.2 with a Full Version Installer

• https://www.mozilla.org/firefox/all/

Please let us know if this solved your issue or if need further assistance.

Thank you for your advice, Pkshadow. I went through those procedures (except that after Unintallation, there were no Mozilla Firefox directories in Program Files, Program Files (x86) or ProgramData), and reinstalled; but I regret to report that the new installation is no faster than the old, and is still unusable.

can you capture a performance profile while the slowness is going on and share it with us? https://developer.mozilla.org/en-US/docs/Mozilla/Performance/Reporting_a_Performance_Problem

I'm trying to do this (but of course everything happens very slowly). I have got as far as capturing the profile, and eventually the green "Share..." button appears as promised. But clicking it appears to have no effect, and no url appears anywhere that I can see. Clicking Save as File is also ineffective.

Apologies for a long silence on this. I was trying repeatedly to get a profile, but Firefox was so utterly slow that I could not get anything out. I have finally succeeded in doing so, and have shared the profile. The URL is https://perfht.ml/2HFbHuM . The sequence of actions that might be represented in the profile was as follows: Started Firefox 59.0.2 Started Gecko (it was in the Stopped state, with greyed-out icon). Response was fairly prompt. Clicked on bookmark in Firefox to browse to Wikipedia. Long delay with nothing visible happening. During the delay, keyed ctrl-shft-2 When the profile eventually appeared (long after Wikipedia had loaded), clicked on SHARE; response was almost immediate. Uploaded profile as suggested. Possibly worth noting: Firefox was running at about 30% of CPU, and using about 1.3Gb of memory, throughout. I don't know whether this is normal on my machine. The problem arises on my desktop machine only. It is clearly machine-specific because I don't get the problem with my laptop, running on the same network. Both machines run fully-updated Windows 10, with Windows Defender the only live virus control. I am fairly confident none of this is connected to profiles because (i) it also happens when my wife is using the machine, on a different user a/c with its own profile and (ii) I have tried creating new profiles in past rounds of this problem, without it making any difference. The machine is connected through a network switch to a Symantec DS214 NAS, which does sometimes cause access delays in software, but nothing on this scale and anyway I can't see why Firefox would be talking to it at all. Many thanks for your interest in this problem. I would dearly like to fix it; I have fallen back on Chrome for the time being, but there is quite enough Google in my life already, and I would much rather be able to go back to using Firefox.

thank you - looks like ibm trusteer rapport that is installed on your system is causing this particular hang...

thank you, philipp. Disabling Rapport did indeed resolve the problem. So I then uninstalled it (pain and grief because it had a stuck .dll, and I had to go into Safe Mode to remove it) and reinstalled it, and Firefox (now upgraded to 59.0.3) and Rapport (version 2.1.24) are now working happily together. So if I get this problem again, I'll try killing Rapport first.

thanks for reporting back with your findings!