Changes in Thunderbird 86

theme

• The theme API was added to Thunderbird (see bug 1684666). It’s more or less the same as the Firefox theme API, but has been extended to better fit the needs of Thunderbird.

  The color key sidebar_highlight_border has been added.

  This change has been backported to Thunderbird 78.7.1.

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Bugzilla list of fixed WebExtension API defects in Thunderbird 86.