Latest Win10 update has blocked Firefox as default browser, locked Edg

Hello CmmTch - I have Dell xps-13 Win10 laptop that I just checked and default browser on it is still Firefox. Here's the thing. It is still on version 1803 of Windows. I know one can uninstall updates but I'm a little afraid to roll back my desktop Windows to 1803. There are at least 6 1809 updates on it. Maybe I can roll back to the time I still could choose default browser which would be April. Do you have any advice? Have you ever uninstalled Windows updates?

Sorry CmmTch. I haven't been clear. I have a new Dell 8930 desktop computer, installed last March. That is the computer I am having trouble with and the one that is completely up-to-date with Windows 10 v1809. I also have a Dell XPS-13 laptop computer that I use mostly for travel. It is the one updated only to v1803.

The trouble with your recommendation that I reinstall Firefox is that when I go to Settings>apps>default apps>web browser ONLY MS Edge is on the list, also "Look for the app in Microsoft Store". In other words, the default web browser choices do not include IE11 for instance, nor Google Chrome, also on my computer. MS Edge is totally locked in, no more choices for me. I don't think reinstalling Firefox would gain me anything.

I just installed Firefox on another machine,
It wouldn't allow me to choose Firefox as default in Settings...



I created an .html file on my Desktop, right clicked it/Properties/General/Opens with:/Change...



Scroll down to...



Navigate to firefox.exe and choose...



Voila...

ATTENTION: I woke up in the middle of the night last night and was mulling over my default browser problem when it occurred to me that on Friday night I ran Auslogics defrag program's "optimize SSD". That could be the problem.

This morning I did a system restore back to May 1st 2019 and, voila, I have my list of browsers back and Firefox is my default browser once again. Hallelujah.

I read that one shouldn't defrag an SSD but some people think it is ok. Well, I thought, what could be the harm. It is harmful.

Attention everyone: Don't fool with an SSD.

Thanks to Edwin, CmmTech and all of you for your suggestions and help.

FWIW I updated Win10 Home from 1809 17763.678 to 1903 Build 18362.295 on a brand new HP All-In-One desktop PC this week when WinUpdates offered the feature update to me a few days ago. Although Control Panel finally offered Firefox on the list and I selected it to be my default, I keep getting the message every time I open Firefox that "Firefox is not your default browser. Do you want to make it your default browser (which I tick)" to indicate yes. But Windows is NOT doing it! Again and again at every opening of FX I get this Windows popup box saying it's not my default browser and again and again I tell it to make it so! So it's not just OP's problem.

PS: I've been using Win7 until this month and have been a member of the Win7 forums for a long time. Just got this new Win10 PC, and on a fast learning curve, so I suspect I'll be visiting here more often now. Heretofore, I just did a lot of passive reading here to get myself up to speed on Win10 and to learn about its foibles before this computer purchase.

- - - Updated - - -

OK, I think I finally fixed the problem. With Firefox open, I went to Tools, Options, General and under START UP, it said Firefox was not my current browser. I clicked to make it my default browser. Then I went into Win10 default apps ONE MORE TIME, and did the same, clicking on the Firefox list option. Then I closed FX and reopened and I no longer get that popup box from Windows saying FX is still not my default browser. Finally!

Just to let you know about a quirk in FF 60 (I'm not updating it), when I want a default htm or html reader to be some other application than FF such as Internet Explorer or Universal Viewer, changing it in the Win 10 Apps setting "choose default apps by file type" removes FF as default browser.