At first, a maintainer considered it to be a regression to implement (reading the bugzilla page), which caused it to be delayed for ~7 years. Then the issue went more or less inactive for almost a decade because the world at large dismissed OpenPGP encryption on mail as pointless (in part due to the complexity in actually getting it working since no mail client gave it a first class implementation, leading to a circular case of it not being implemented because nobody did it.)
2 years ago it was deliberately revived by Mozilla, then it devolved into bikeshedding about the design and now it's finally shipped.
2 years ago it was deliberately revived by Mozilla, then it devolved into bikeshedding about the design and now it's finally shipped.