Review for Expression (Power) Message Search - NG by Thomasd du Nord
Rated 4 out of 5 stars
It's great, but for some reason it stops working every now and then. For the people that can't get it to work at all, try installing it from the add-on page: https://addons.thunderbird.net/nl/thunderbird/addon/expression-search-ng/?src=ss - that seems to make it active.
This review is for a previous version of the add-on (3.6.3).To create your own collections, you must have a Mozilla Add-ons account.