Actually, it will annoy me in particular even though FF is my default browser. Technically, Choosy (https://www.choosyosx.com/) is my default "browser" on macOS and FF is the preferred browser in Choosy. I hope there will be an about:config preference to disable "nudging".
Even better they should embed this Choosy functionality inside firefox as an option. Eg: I'm on firefox and I click on a link that contains a domain that I would to open on a different browser. I admit this is a very power user feature but not much different than this precisely default browser thing: it affects only multi-browser users (which would love to jump out of firefox based on some rules, guess there is already an extension for it).
So if you enable `browser.newtabpage.activity-stream.asrouter.devtoolsEnabled` you can navigate to `about:home#asrouter`, look for `INFOBAR_DEFAULT_AND_PIN_87` (that's the ID for this message) and click BLOCK.
It's best to flip the pref back cause it might cause issues (and this won't revert the block).
I swear I had this idea! (I mean choosy) Perhaps it's a natural conclusion. Another similar idea is auto-sorting downloaded files (and extracting archives, also acting on the origin by reading the FF sqlite DB, etc.)
