Dave-H

Icaros is a very good thumbnailer system, as it allows explorer to generate thumbnails from many video formats which aren't natively supported. If you didn't install it that can't be the problem though! ASF is a Microsoft media video/audio format, pretty much the same as WMV, but IIRC was more often used for streaming. I would have thought that it's pretty obsolete now.

I suspect that a shell extension could well be causing this. It triggers when you select certain files, and crashes explorer. Download this (it's free and quite safe). It will give you a list of all the shell extensions installed. Any that you are suspicious of, especially any related to K-Lite (perhaps a thumbnailer) or WMP, disable them and see if things are then OK. If the problem goes away, re-enable them one by one until you find the culprit. HTH.

Thank you. 1.16.4.18 seems to be still working fine. I've also suppressed the warnings in the add-ons list using an addition to the userContent.css file I was already using to get the videos on Instagram to display.

Well it does seem to be a bit of a mish-mash of posts about the "viewtube" extension and viewing YouTube videos online in WMP! How about - "Viewing YouTube videos with the "ViewTube" browser extension and XP Windows Media Player"

Thanks, again good to know more of the background to this. I've uninstalled 1.17.4 and installed 1.16.4.18 instead. Seems to be working fine except for the annoying warning in the add-ons list that it can't be verified.

FWIW I don't think the recent discussions about using WMP to view YouTube videos should be in this thread anyway, as it was originally specifically about enabling them in older Firefox browsers on XP. When does explorer crash, is it while you're doing something specific, or are the crashes just seemingly random, and happen even if there is no explorer window open?

Thanks for the detailed background explanation @Mathwiz! So, is there any disadvantage with using 1.17.4, which presumably will not now update any more on FF 52 ESR? As long as it's still getting block list updates does it matter that 1.16.4.18 is actually later code? Have any security flaws been patched which are in 1.17.4 for instance? Cheers, Dave.

I think you actually just answered the question. I was thinking that some people were using 1.16 instead of 1.17 because 1.17 didn't support their browsers. From what you say that does seem to be the case, but 1.17.4 is still the latest version for Firefox 52 ESR. Is that right, or are you saying that 1.16.4 actually has more up to date code in it than 1.17.4 (I don't mean the block list files)?

So who's developing it, and why would they concentrate on an older version instead of the last FF 52 ESR compatible version? Does 1.16.x support even earlier browser versions?

I don't understand, I'm already using 1.17.4, which is surely even newer! Are we talking about the same thing?

I love Microsoft's suggested workaround to avoid the problem. Basically, just don't do it! Thanks again @jaclaz, you've given me a lot to get my head around here, but that's what this forum is all about of course. Cheers, Dave.

Thanks again, as I'm sure you're now well aware, I have only ever gone into the intricacies of disk partitioning at a very basic level! So if I read your analogy correctly, extended partitions are like they're in a container, into which utilities like mbrwiz cannot read? For some reason lost in the mists of time, I have always formatted my data drives as extended partitions, my only primary partitions are the system drives for Windows 98 and Windows 10. Disk 2, the Windows 10 drive, was partitioned by Windows setup, and both partitions are primary. The Windows XP partition on disk 1 isn't, it's an extended partition. Is there any disadvantage to the data drive partitions or the Windows XP partition being primary partitions, presumably as long as they're not set active?

Thank you, I'll have to read that a few times to get my head around it, but I should have of course made the connection that the partitions concerned were extended partitions, not primary ones! Is it normal for MBRWiz not to see the drive letters and volume labels of extended partitions?

Well I'm glad you found a workaround anyway, although the performance hit on Firefox after it's been open for a while, even with a completely clean profile, is very puzzling.

@jaclaz Not wishing to hijack this thread, but as someone with three SDDs on my system and two conventional drives, I just tried this out myself, just out of interest. This is what I got - The two SSDs that are partitioned, disk 1 and disk 2, both show the start of the first partition as 2048, which I assume is good. Disk 3 is also an SSD, but shows its single partition start as 16065. Is that OK? Disk 0, a conventional FAT32 IDE drive, also shows 16065, and disk 4, a conventional FAT32 SATA drive connected via an expansion card, shows 16321. Also slightly puzzled that I'm only seeing drive letter and label information for two of the partitions, is that normal?

This is all I'm seeing on Firefox 52.9.1 ESR. Nothing very useful!

If that's the case, I'm certainly on borrowed time!

Two updates today, KB4484267 for Excel, and KB4484163 for Outlook. Both installed with no problem and everything is fine. Still a very long scan on Microsoft Update, but it got there in the end!

I assume you have add-ons? If Firefox is slowing down even when it's apparently not being used, it could be an add-on working in the background that's doing it. Try running Firefox with add-ons disabled (under the help menu) and see if it slows down if it's left alone like that.

As AVG and Avast are now the same company, I don't see how one can be considered OK and the other "discredited"? When I tried them both they seemed to be virtually identical.

But am I right in assuming that your original installation of non-ESR Firefox 52 didn't have this scrolling problem? If so, I wouldn't have thought that it was an intrinsic problem with the graphics hardware. More likely it is a configuration issue somewhere in the new version of Firefox. As you seem to have tried a lot of different settings parameters, and there is always a chance that settings can interact, so changing just one wouldn't necessarily affect the problem, I would try resetting all the configuration options to their defaults and see if the problem is still there then. To be safe, take a backup of your Firefox profile folder, and then if you get into trouble you can always restore it to get your present configuration back.

OK, well the other variable in the system is your graphics card of course. The visual performance of browsers is very dependent on how they interface with the machine's graphics, especially when it comes to things like playing demanding videos. Of course that doesn't explain why your original installation of non-ESR Firefox 52 presumably didn't have the problem, with the same hardware. I have a very old video card. I do have "Use hardware acceleration when available" ticked, but I suspect that it isn't actually available! The symptoms sound like a buffer is getting full or something like that, and re-starting the browser clears it.

FWIW I've never noticed any scrolling problems on FF 52.9.1 ESR. It always seems to be fine to me. The problem must be due to running it in the sandbox I would have thought.

I found that enabling multiprocess on 52.9.1 ESR made a very big difference to performance on things like Facebook pages. It was well worth doing! Glad to hear that slack is still OK. As I said, I don't know anything about sandboxie, but is it possible that when Firefox is running in it, and it tries to run another program (in this case plugin-container.exe) that sandboxie might treat this as a possible threat, and block it?

Yes, "plugin-container.exe" runs for me when I load a YouTube page, and stops when I leave it, so it's definitely needed. If it won't run under sandboxie I'm afraid I don't know what to suggest, as I have no experience of that. If there is a forum for sandboxie users, perhaps you could ask there. Did you try "slack" on your temporary 52.9.1 installation BTW, did it work?