FirefoxPortable on Windows 10?

I am using FirefoxPortable v88. This works perfectly under Windows 7 but when the same flash drive is started using Windows 10 64-bit I receive the following message:

"You've launched an older version of Firefox
Using an older version of Firefox can corrupt bookmarks and browsing history already saved to an existing Firefox profile. To protect your information, create a new profile for this installation of Firefox.
[Exit] [Create New Profile]

Of course creating a new profile means loosing not only bookmarks and browsing history, but apparently all add-ons and themes as well. At least some of the files associated with the previously-installed add-ons appear to have been deleted from the \PortableApps\FirefoxPortable\Data\Profile folder.

FirefoxPortable then creates a directory structure containing hundreds of files in:
"C:\Users\%USERNAME%\AppData\Local\Mozilla"
"C:\Users\%USERNAME%\AppData\Roaming\Mozilla"
"C:\Users\%USERNAME%\AppData\Local\Temp\Firefox"

If a regular non-portable version of Firefox is already installed on the host computer, of course it will have already created the folders above; and in that case FirefoxPortable seems to use those folders.

Going to about:profiles and attempting to [Set as Default Profile] and [Restart] simply goes back to the warning above and requires creating yet another profile.

So FirefoxPortable is no longer really portable under Windows 10?