I have implemented the new start page in Bug 1103396 and noticed that the Add-ons link is opened in Firefox, my default browser. It would be nice if Thunderbird could open the link in its own window, maybe by whitelisting www.mozilla.org to open about:addons, so the users can easily install extensions and themes.
Or just by supporting <a target="_tab">
xref bug 318104
Summary: Provide a way to open a new tab from the start page → Provide a way to open add-ons links on Thunderbird start page in a Thunderbird about:addons tab
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