> the only big loss was UI manipulation Well, for a start e.g. mass downloaders have become relatively useless because they can't download to outside of the OS

> the only big loss was UI manipulation Well, for a start e.g. mass downloaders have become relatively useless because they can't download to outside of the OS downloads directory without resorting to weird hacks, can no longer intelligently handle already existing files, etc. Then user scripts no longer being able to live normally on the file system (and therefore being editable outside of whatever limited UI the extension can provide, being easily searchable) are another victim of webextensions.