Cannot use about: links in the show-heartbeat Learn More link

[Osmose]

Bugzilla: Bug 1346198

If you try to use an about: link as the URL for the "Learn More URL" field in show-heartbeat recipes, clicking the link fails with the following error message:

11:02:31.696 Error: Cannot open a about: link using the text-link binding. 1 text.xml:328
	open chrome://global/content/bindings/text.xml:328:15
	onxblclick chrome://global/content/bindings/text.xml:377:1

[mythmon]

The fix here would probably have to be detecting about: links and adding our own click handlers to the link to open the correct page.

[Osmose]

Adding a useoriginprincipal attribute to the element may also fix this; we had to do that for the link to about:studies in about:preferences.

[mythmon]

Closing in favor of bug 1346198.