Default apps

We have a couple of add-ons that do it now. eXpresso and Portable File Associations. The former intercepts double-clicks in Explorer and other locations and then passes it off to the portable app, but it doesn't work with in-app stuff (clicking links in your email client, clicking the URL link in your password manager, clicking Help in the About menu of an app, etc). The latter (PFA) works by associating at the file system level and then setting it back on exit. We had planned to use this approach in the platform proper and have most of the code done to do so, unfortunately, Windows 8/8.1/10 basically disallowed it from working. You can associate at the Windows level, but it will still ask the user and default to the old association. Windows was changed to prevent apps from stealing associations. Something like portable file associations would be considered stealing an association without user input.

So, we're likely going to implement a hybrid of the two at some point, but it's still being mapped out. Until then, you can use one of those add-ons from the forums.