[#883489] ensure we clear the details bar on default pages.
[#883489] ensure we clear the details bar on default pages.

humphd/thimble.mozilla.org,humphd/thimble.mozilla.org,mozilla/thimble.mozilla.org,humphd/thimble.mozilla.org,mozilla/thimble.mozilla.org,mozilla/thimble.mozilla.org,humphd/thimble.mozilla.org,mozilla/thimble.mozilla.org