Pin messages to stay always on top with Thunderbird

How can I make Thunderbird to pin selected emails to stay always on top?
I can't find this feature in Thunderbird, there is a pin icon but it looks like it only "keeps the filtering when changing folders", whose function is not too clear to me. Also, suggestions on this (and possibly other) add-ons are welcome.

It does not work this way in Thunderbird. Instead you can "Star" messages, then use "Quickfilter" to quickly only displays the starred messages to give them attention. Works very intuitive and efficiently as well, a bit as the labels in gmail.