Install Firefox again with a full installer. You shouldn't lose any data.

The full offline setup for Windows can be downloaded from https://www.mozilla.org/firefox/all/#product-desktop-release as downloading Firefox from Windows from mozilla.org may serve you the small online stub installer.

An error message like XPCOM missing or about platform version or entry points not found can happen because of a failed Firefox update that left you with a mixture of old and updated files in the Firefox installation folder.

This can happen in case security software was keeping a handle of some of the files in the Firefox program folder preventing Firefox from replacing all the files. You need to reinstall Firefox and possibly remove the Firefox program folder to ensure that all files are replaced.

You may have to disable security software temporarily in case the problem persists.

Ok, I'll try that. I am not computer savvy at all. When I click on the link I have to answer some questions. How do I find out what my preferred installer is, please?

Firefox for Windows 64bit.

OK, I'll give that a whirl. Thank you.

I've downloaded Firefox 64 bit. I've installed it. The computer desktop now shows two shortcuts for Firefox. The new shortcut works but it has nothing from the old version of Firefox. so it's a fresh version. How do find the old Firefox information to copy to this new Firefox?

When I go to C:\Users\DellLaptop\AppData\Local\ I see two folders. One is the old Firefox and is called Mozilla, dated 12/08/2024 The second is called Mozilla Firefox, dated 26/06/2024 ...................................................................................................................................

The old version (ie Mozilla 12/08/2021) has one folder and this is called Firefox. I open Firefox (dated 26/06/2024) and this has two folders. One is called Profiles, dated 26/06/2024 14:18 The other is SkeletonULock-35c74239, dated 26/06/2024 14:20 [While copying this data onto this message, a new folder has appeared. This third folder is called SkeletonULock-c388d246]

Profiles has 3 subfolders. The first is nwjarhwd.default-release, dated 26/6/2024. This has 10 subfolders

The subfolders are: cache2.2024-06-26-07-43-40.purge.bg_rm, dated 26.06.2024 08:43 jumpListCache, dated 25/06/2024 20:45 personality-provider, dated 15/08/2021 11:43 safebrowsing, dated 26/6/2024 08:35 settings, dated 12/08/2021 17:13 startupCache, dated 26/06/2024 08:13 thumbnails, dated 25/06/2024 17:23 activity-stream.discovery_stream.json, dated 26/06/2024 08:18 activity-stream.personalization.json, dated 18/05/2024 18:58 activity-stream.weather_feed.json, dated 26/06/2024 08:43

The second is pwiz4m30.default-release-1, dated 26/6/2024 This has 6 subfolders: cache2, dated 26/6/2024 14:35 safebrowsing, dated 26/06/2024 14:51 startupCache, dated 26/06/2024, 14:20 thumbnails, dated 26/06/2024 14:18 activity-stream.discovery_stream.json, dated 26/06/2024 15:05 sctivity-stream.weather_feed.json, dated 26/06/2024 14:19

The third is xrq3g7be.default, dated 12/08/2021. This is empty. ........................................................................................................................

Now about the new Mozilla Firefox. This has a bazillion folders. There's too many for me to list. Unless you tell me to do so, I'll leave this for now. ..........................................................................................................................

So what do I do now? The new desktop shortcut to Mozilla Firefox works but it doesn't have my open tabs nor my book marks etc.

Enter about:profiles in the address bar and find your old profile.

Obviously I can only do this with the new Mozilla Firefox. What I see is the following:

About Profiles This page helps you to manage your profiles. Each profile is a separate world which contains separate history, bookmarks, settings and add-ons.

Restart Restart with Add-Ons Disabled... Restart normally...

Create a new profile

Profile: default-release Default Profile no Root Directory C:\Users\Dell laptop\AppData\Roaming\Mozilla\Firefox\Profiles\nwjarhwd.default-release Open folder Local Directory C:\Users\Dell laptop\AppData\Local\Mozilla\Firefox\Profiles\nwjarhwd.default-release Open folder Rename Remove Set as default profile Launch profile in new browser

Profile: default Default Profile no Root Directory C:\Users\Dell laptop\AppData\Roaming\Mozilla\Firefox\Profiles\xrq3g7be.default Open folder Local Directory C:\Users\Dell laptop\AppData\Local\Mozilla\Firefox\Profiles\xrq3g7be.default Open folder Rename Remove Set as default profile Launch profile in new browser

Profile: default-release-1 This is the profile in use and it cannot be deleted. Default Profile yes Root Directory C:\Users\Dell laptop\AppData\Roaming\Mozilla\Firefox\Profiles\pwiz4m30.default-release-1 Open folder Local Directory C:\Users\Dell laptop\AppData\Local\Mozilla\Firefox\Profiles\pwiz4m30.default-release-1 Open folder Rename

Many thanks for your help.

Firefox uses two locations in the hidden "AppData" location for the Firefox profile folder. One location in "AppData\Roaming" for personal data like bookmarks and logins and another location in "AppData\Local" for temporary files like the disk cache, so make sure to look in the correct location.

• https://support.mozilla.org/en-US/kb/recover-user-data-missing-after-firefox-update

Am I correct in thinking I will get Mozilla Firefox up and running with my old data if I do this: 1) I go to "about:profiles"; 2) I go to Profile: default-release; 3) under the data in that box, I click on "Set as default profile"

And that should do the trick? Yes?

That's right.

Yay! I've just done that and it works. I've got my old stuff back with the new Mozilla browser. Many, many thanks TyDraniu.

Can I ask a further question here, please, despite my original question being satisfactorily answered.

I've now deleted the shortcut icon for the old Mozilla Firefox from my desktop. Firefox is not one of the programs on start-up - I've checked this. But even when I do not use Mozilla Firefox. I keep getting this pop-up with the Firefox icon showing on my taskbar at the bottom of the screen.

XUL Runner Error Platform version '127.0.2' is not compatible with minVersion >= 127.0.1 maxVersion <= 127.0.1

How do I make this go away (other than pressing the X at the top right hand corner)? I suppose it's no big deal to have to have to press the X but I much prefer that it doesn't show up.

An error message like XPCOM missing or about platform version or entry points not found can happen because of a failed Firefox update that left you with a mixture of old and updated files in the Firefox installation folder. This can happen in case security software was keeping a handle of some of the files in the Firefox program folder preventing Firefox from replacing all the files.

You need to reinstall Firefox and possibly remove the Firefox program folder to ensure that all files are replaced. You may have to disable security software temporarily in case the problem persists.

• https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

Reinstall Firefox:

• https://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems

Gosh! That looks complicated.

I think I have two versions of Firefox on my computer. The old version has the corrupted files and the new version has the pristine files. I need to remove the old version.

Maybe I'll stick with what is working now and put up with the annoying pop-up. It's not a big deal to press the X to close the pop up, which does not turn up that often.

Thank you for your time and trouble.

You only need to download the full Firefox installer from the Mozilla server and install this version.

• https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

I have done that already. That's why I now have a brand new pristine version of Firefox. I have added my old profile to this updated Firefox which means I can use that browser. My problem is that the installation of the updated new version of Firefox didn't impact the old existing corrupted Firefox I had on my computer. So that is why I believe I have two versions of Firefox on the same laptop. And it's the old corrupted Firefox which keeps generating the XUL Runner message at least once a day. If I have to live with this, I can, because it only pops up once a day, or maybe twice. So unless someone tells me how to delete the old corrupted Firefox, I will just have to accept I must cross the X on these XUL Runner pop-ups at least once a day. Or just ignore them when they appear. I suppose I can get used to seeing these messages.