Bugzilla

Also helpful: https://en.wikipedia.org/wiki/List_of_URI_schemes

I've highlighted some schemes when entered in the urlbar have a unique interaction with the browser. 
- `callto` - `callto:<screenname>`
- `view-source` - `view-source:https://www.example.com/`
- `message` - `message:example`
- `sms` - `sms:+15105550101?body=hello%20there`

And map features:
- `bingmaps` - `bingmaps:?cp=47.36667~8.55` - Possibly Windows?
- `geo` - `geo:40.726966,-74.006076` - Tested on Android
- `maps` - `maps:q=<physical location>` - OSX

For completeness I also tried looking at all the schemes, which are probably not relevant to our case:
- `acct`
- `acr`
- `afp`
- `aim`
- `amss`
- `barion`
- `bitcoin`
- `cid`
- `dab`
- `dav`
- `dns`
- `drm`
- `doi`
- `example`
- `fax`
- `feed`
- `fm`
- `gg`
- `gtalk`
- `h323`
- `iax`
- `icon` - Mozilla uses  moz-icon://, but there is also another `icon` uri spec
- `im`
- `info`
- `iotdisco`
- `ipn`
- `iris`
- `jabber`
- `jar`
- `jdbc`
- `jms`
- `magnet`
- `mid` 
- `msnim`
- `ms-settings`
- `mvn`
- `oid` 
- `opaquelocktoken`
- `openpgp4fpr`
- `palm`
- `pkcs11`
- `platform`
- `pres`
- `proxy`
- `query`
- `service` - may have double slashes for a resource it's referencing
- `session`
- `shc`
- `sip` and `sips`
- `skype`
- `spotify`
- `steam`
- `stun`, `stuns`
- `tag`
- `things`
- `thismessage` - uses one slash
- `trueconf`
- `turn`, `turns`
- `tv`
- `web+`
- `ws`, `wss`
- `xcon`
- `xfire`
- `xmpp`
- `ymsgr`

Also helpful: 
- https://en.wikipedia.org/wiki/List_of_URI_schemes
- https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/protocol_handlers
- https://searchfox.org/mozilla-central/rev/cda5e5c662c2e0da5ee63dc4669899e3ed4ccb18/dom/base/Navigator.cpp#880

One thing we were missing that loads in the browser:
- `view-source` - `view-source:https://www.example.com/`

Map features:
- `bingmaps` - `bingmaps:?cp=47.36667~8.55` - Possibly Windows?
- `geo` - `geo:40.726966,-74.006076` - Tested on Android
- `maps` - `maps:q=<physical location>` - OSX

I've highlighted some schemes that can use no slashes and entered in the urlbar have a unique interaction with the browser, namely they're mentioned in the code, or will launch an external application:
- `bitcoin` - `bitcoin:mjSk1Ny9spzU2fouzYgLqGUD8U41iR35QN`
- `callto` - `callto:<screenname>`
- `im` - `im:pepp=example.com/fred@relay-domain`
- `message` - `message:example`
- `sip` and `sips`
- `sms` - `sms:+15105550101?body=hello%20there`
- `smsto`
- `xmpp` - `xmpp:foo@example.com`

Other applications can be launched via keywords, too many to list here: https://searchfox.org/mozilla-central/rev/cda5e5c662c2e0da5ee63dc4669899e3ed4ccb18/toolkit/mozapps/handling/ContentDispatchChooser.jsm#37