Register outlook.office.com in the browser as a protocol handler for "mailto:" links
Firefox (v68) already recognizes Gmail and Yahoo! Mail as valid handlers for "mailto:" links. It would be awesome if outlook.office.com would also register itself as being able to handle "mailto:" links.
I would even get the ability to make Firefox "ask everytime" I click on a "mailto:" link and then select between Gmail or my work Outlook. Or any locally installed email client. Perfect!
It should be not at all difficult for the fine people at Microsoft to build this: https://developer.mozilla.org/en-US/docs/Web/API/Navigator/registerProtocolHandler/Web-basedprotocolhandlers
For me, this is the one missing feature to make the Outlook desktop client totally redundant! All the bells and whistles I need are in the web version! For which: big kudos!