I created a regular user account for the person who'd be using this system, then used Windows Transfer to move account settings and files from the old Windows XP system. I also created one other regular account, for me to use as well as a third admin level account. When I use "my regular" account, Mozilla app icons display just fine. The locations are: taskbar, Start menu and in Windows Explorer window opened on "C:\Program Files (x86)\Mozilla Firefox" and "C:\Program Files (x86)\Mozilla Thunderbird". When I go to the other user account, all the "icons", in *all* locations, are white rectangles, with what looks like a "generic window" graphic. This looks to me like a permissions problem, preventing the window environment from reading the icon image from whatever file the image is stored in. I don't know the name of the file which contains the icon image, so I can't check this. I can say Firefox and Thunderbird both run fine in all accounts. I just installed the 'troubleshooter' add-on, but note that I did this from a properly running setup, and as an admin user. It may not provide anything useful. I want/need to have those icons display properly. Everything else installed is fine, including other third party software.