might work. maybe... Rated 2 out of 5 stars

the mentioned calculation is workin in the quicksearch bar...but thats the only thing.
searchkeywords like f:foo or from: foo won't find any existing mail in the current folder. tried with tb 2.0.0.18 developer stoped developing in 2007 maybe thats the reason.
also you cannot unbind any keyboard-shortcut, which is really annoying. everytime you press the Y-key, this extension deletes a message (if no archive folder is created before, which is not, because I DO NOT NEED AN ARCHIVE FOLDER, BECAUSE I DO NOT ARCHIVE MY MAILS)
so 2 stars because of the name google...

This review is for a previous version of the add-on (0.6).