The TB addon called ThunderBrowse - https://addons.mozilla.org/en-GB/thunderbird/addon/thunderbrowse/ - is listed as a “Featured” addon and it shouldn’t be. It was last updated in 2012 and only works with Thunderbird 1.5 - 16.*, we are well past that version.
There are over 100 complaints about the addon being broken.
This needs immediate attention !!