Very nice, but sometimes not working Rated 3 out of 5 stars

March 24, 2012 (update): A developer contacted me regarding my (now retracted) post that this extension doesn't seem to work anymore (TB 11.0). After further testing I found it does still work, just not always. Output from error console on failure:
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Error: uncaught exception: [Exception... "Component returned failure code: 0x80004003 (NS_ERROR_INVALID_POINTER) [nsIMsgDatabase.GetMsgHdrForKey]" nsresult: "0x80004003 (NS_ERROR_INVALID_POINTER)" location: "JS frame :: chrome://followreply/content/followreply.js :: <TOP_LEVEL> :: line 27" data: no]
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This error is generated from Follow Reply (FR) on an email in the Inbox Group in which the reply is in the IMAP Sent folder. A search function isn't even started by FR. A reply is found on this mail if FR is performed in the account Inbox folder, but FR does work from other grouped folders.
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January 23, 2012: Very nice, indeed, even if exceedingly slow on IMAP accounts having a lot of folders. The performance could be improved by being able to specify which folders should be searched for replies and a possibility to cancel a lonnnngggg search.
It would be great to see this developed further!