Review for Expression Search / GMailUI by v56k
Rated 5 out of 5 stars
Like everyone else have had to drop back to 60.9.1 which I believe is the last version to support this ESSENTIAL add-on.
Really hope the developer is still active - have sent my $5 and now keeping fingers crossed.
For me Thunderbird is unusable without this search ability - hence the downgrade.
To create your own collections, you must have a Mozilla Add-ons account.