Pretty sure like 1% of add-ons are actively monitored by Mozilla, and using the username chosen to criticize free software is ridiculous. For example, darktrojan is a member of the Thunderbird core team, see https://wiki.mozilla.org/Modules/Thunderbird
Hm, well I'm sure it's by a well-known and trustworthy author.
"The source for this add-on is at https://github.com/darktrojan/openwith."
Dark Trojan. Sounds legit.