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CloseReview for FireTray by Zverik
Rated 5 out of 5 stars
Great add-on, though suffers from some bad management decisions. To restore old tray icon (with left click and message count), open preferences, "advanced→config editor", find "with_appindicator" and set it to false. Then restart Thunderbird.
Source: https://github.com/foudfou/FireTray/issues/147#issuecomment-68603942
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