I have installed Firefox (and other "user" programs) on a distinct HDD from where Windows 10 is installed, and I believe this is why when I try to set Firefox as my default browser, it is not listed as an option when the uSoft Settings screen is presented. Using: > dism /online /Export-DefaultAppAssociations:"f:\Users\Bob\Temp\MyDefaultAppAssociations.xml" in Powershell, I am able to view current app associations, and with a little luck, I should be able to edit that file and import using something like: > dism /online /Import-DefaultAppAssociations:"f:\Users\Bob\Temp\MyDefaultAppAssociations.xml" To the editing, if I search for an Association Identifier such as .htm, I currently find: <Association Identifier=".htm" ProgId="AppX4hxtad77fbk3jkkeerkrm0ze94wjf3s9" ApplicationName="Microsoft Edge" /> To edit this entry, I need two things, being the correct ProgId and ApplicationName. I am not convinced [yet] that ProgId can be something as simple as "FirefoxHTML" (in this case); rather probably needs be some registry value. Has someone already solved this problem, or is there a proven process already written, or am I off in the weeds, and doomed to uSoft browsers by default unless I redesign the way I have laid out O/S, apps and user files on my system? Thx in advance ...