I had to re-install Windows 10 from scratch and then all my programs. I downloaded Thunderbird 60.0 and linked to my old profile. All folders are there and mail works fine. I have no enabled themes or extensions. If I go to the add on tab I can see tons of themes. If I click on a link for one it takes me to that theme's page. Then if I click on the "+Add to Thunderbird" button it takes me to a page (ex. https://addons.thunderbird.net/en-US/thunderbird/addon/10900/) saying " We're sorry, but we can't find what you're looking for." If I go back to the list of themes and hover over one, there is a grayed out "+Add" button that does not work. So how do I add a theme or extension? I tried many at random and all had the same results. Thank you.