Problem with default browser

Firefox has always been my default browser but today I started it and for no apparent reason it says it's no longer the default browser so I reconfigure it as default, but whenever I close FF and relaunch it it says again it's not the default browser.

Help please.

Hello Read Only,

Double check in Default Programs to make sure that Firefox is set as the default program with all of it's defaults (associations) set for it as well. Afterwards, see if Firefox is still says that.

Hope this helps,
Shawn

I tried that but that didn't help
Still the same problem, I wonder if it's not a registry corruption

If Firefox shows as "This program has all its defaults" in Default Programs like in the first screenshot below, and Firefox opens by default when you open a internet shortcut (Favorites/Bookmarks), then you could click on Tool -> Options in Firefox to uncheck the option in the second screenshot below to stop that message.
If you also use Internet Explorer, then you might also uncheck the same option below in Internet Options to not if it check to see if IE is the default program as well.

these parameters remove the "default browser" prompt each time so it's all good, but it doesn't really solve the problem which is that setting a default browser does not work.

Is Firefox showing "This program has all its defaults" in Default Programs?

If so, then it really doesn't matter since Firefox is actually already set fully as the default program.