https://services.addons.thunderbird.net/EN-uS/thunderbird/addon/reminderfox/
ReminderFox :: Add-ons for Thunderbird
ReminderFox displays and manages lists of reminders and tasks. ReminderFox uses easy-to-use lists with warnings/alarms to remind you of all your important...
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https://groups.google.com/g/reminderfox/c/MlYIeFOtpMs/m/0RiFOQbuAwAJ
ReminderFox support nearing an end (ThunderBird 65)
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https://reviewers.addons.thunderbird.net/En-US/thunderbird/addon/reminderfox/versions/?page=1
ReminderFox :: Versions :: Add-ons for Thunderbird
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https://reviewers.addons.thunderbird.net/eN-US/seamonkey/addon/reminderfox/reviews/774942/
ReminderFox :: Reviews :: Add-ons for SeaMonkey
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