Dave-H

OK, it's fixed! The portable version worked fine, and in fact if I ran the firefox.exe in the portable version's program folder, rather than firefoxportable.exe, it opened fine using my normal Firefox profile! So, I started comparing the two installations, and found that some DLLs in my Firefox program folder appeared to have been disabled by renaming 'DLL' to 'D~L'. That's my normal way of disabling a file, changing the middle character of the extension to '~'. Why I had done that is lost in the mists of time in this case, but one disabled DLL file stood out, and that was msvcp140.dll, which is a C++ Runtime file of course. That reminded me that I had recently updated my C++ 2015-2019 Runtime to 14.29.30139, following a recommendation elsewhere on MSFN. Thinking perhaps this could be the issue, I simply renamed the msvcp140.dll file in the Firefox folder back to normal, and everything came good! So, I guess the new system runtime file versions may not actually be compatible with all programs, so I will now be on the lookout for any other seldom-used programs which no longer work. Thanks everyone for the help as always! Cheers, Dave.

No, Firefox was not open when I uninstalled Malwarebytes. I hardly ever use it now. Thanks for the link to the portable version, I will give it a try and report back.

OK, I tried disabling the current Firefox profile (by renaming its folder and making a new empty folder with the same name). Firefox still didn't start, with the same immediate error. I think that means the issue is nothing to do with anything in the profile.

There is no noticeable increase in startup time with 22.03.05 on my machine, it seems perfectly normal as it was before Panda was installed, so I can only assume that it just doesn't run well on your particular hardware.

I did wonder about extensions, I haven't changed those on FF 52 for years, but they do update themselves so it's possible that an incompatibility has crept in. It won't run in Firefox 'safe mode' either though, which I thought was supposed to not load any extensions or plugins. I'll try with a new clean profile which should eliminate this possibility.

Here's what Dependency Walker says. CreateThreadpoolWork is indeed showing an error, but so are several other functions, and they're not stopping it from running! Incidentally, why does it say 'Not Bound'? Should that actually be 'Not Found' or is that terminology correct? Sorry, I'm no expert on this sort of thing!

Thanks everyone, and sorry for the delay in replying. I was having terrible problems accessing the site yesterday, which i hope is now fixed. @NotHereToPlayGames I ended up uninstalling Malwarebytes in Safe Mode because when I tried in normal mode, when I said yes to 'do you want to uninstall' the machine immediately rebooted! Rather than try again and probably have the same thing happen, I then tried in Safe Mode, and it immediately uninstalled, very quickly indeed. Why the machine rebooted, I have no idea. I doubt this has anything to do with Firefox now failing to run, but you never know! @schwups @NotHereToPlayGames I'm not running any form of extended kernel. @ED_Sln Firefox.exe looks to be OK. Very strange. Just to add that Firefox won't run in its own 'safe mode' either.

I do have Revo installer, if you remember I used it to give AstroSkipper a list of .NET updates in another thread. I don't think I've ever actually used it to uninstall anything though! If I did, it would have been a very long time ago, so not related to this issue I'm sure. I have recently uninstalled Malwarebytes 3.5.1 though, using the normal uninstallation routine in Safe Mode. I wonder if there's any connection there?

PortableRegistrator 1.5 certainly works with XP, I don't know about any later versions. I can upload it for you if you can't get a version which works. FWIW I use the Classic Blue theme, which always looks very pleasing to me, but it may not help with your issue of course.

I've had Firefox 52.9.1.6822 installed on the XP side of my machine for many years, as the last Firefox version which will run on XP. I don't use it often now as I use a much more up-to-date version of Supermium. However, I tried to run it today, and it won't run any more. I just get a popup saying - "The procedure entry point CreateThreadpoolWork could not be located in the dynamic link library KERNEL32.dll." Anyone any idea why it would have stopped working? I've not knowingly changed anything relevant since I last used it. The Firefox files seem to be as they have always been, and no system files have been knowingly changed either.

That would certainly make sense and explain things. Version 21 presumably uses IE's proxy settings, and version 22 (and presumably 23) do not, which is why I had to manually set version 22 to use the proxy to get access to my account in its interface.

That's right, but does Panda Dome therefore use the proxy even if its proxy settings aren't set up to do so? And there were no Panda server accesses recorded in the proxy console.

I'm pretty sure that my Panda Dome 21 did activate without using HTTPSProxy, even though I have it installed, and it accessed my Panda account fine too. Version 22 again activated fine as a free version, and updated fine when my Essentials activation code was put in. The only thing it would not do until I put the proxy settings into it was access my Panda account, which 21 had done fine apparently without the proxy.

When I first said that I'd installed Panda Dome 21, and you mentioned HTTPSProxy as being necessary for it to connect on XP, the first thing I did was to look at the proxy console. There were no entries for Panda servers at all, and the program seemed to be working perfectly, connected to my account and activated. How it worked without it, I have no idea. The Panda Dome proxy settings were still on their defaults, whatever they are. I have the proxy set to work system-wide, but it would surely have recorded something in the console if Panda Dome had used it. I have never emptied my Certs folder, or updated cacert.pem, and I've been using the proxy now for several years, as you know! It seems to still be working perfectly. What would be the symptoms if it wasn't because I hadn't done all that. My Certs folder has 4,145 files in it BTW!

Glad you like Supermium, I've been using it for ages now on XP, and it's become my standard browser even on Windows 10. To answer your questions - 1. Unfortunately, Supermium has no internal mechanism to set itself as the default browser on XP. It can be done with a lot of tedious registry editing, or by using a utility like PortableRegistrator. https://www.majorgeeks.com/files/details/portable_registrator.html 2. This one is easy! Just type chrome://flags/#custom-ntp into the address bar, enable it, and fill in the URL that you want your new tabs to display. Restart the browser and there you are! 3. All I can suggest for that is to try different themes. Hopefully one of them will make things more readable for you. I'm sure that almost everything can probably be customised if you know how, but I don't have that level of knowledge of Chromium customisation I'm afraid. Cheers, Dave.