Safari 10.0.2 now blocks custom URL schemes

URL schemes are widely used by many apps to ease the workflow. By example, Little Bookmark Box uses a URL scheme in the bookmarklet and the Safari Extension to send the data about the page you want to bookmark to the Little Bookmark Box app.

Starting with Safari 10.0.2, every invocation of a custom URL scheme displays a warning like this:
scheme warning

Unfortunately, it seems that Apple has forgotten to provide a way to “Always Allow” a particular app or URL scheme, so this warning is displayed each time a custom URL scheme is used.

This new “feature” has been already reported as a bug by other developers. However, for the time being, I am sorry to say that there is neither a fix nor a workaround available. I am hoping that Apple will fix this in the next version of Safari.