Stop the viewBookmark button from displaying nonsensical link during document load

This PR fixes [bug 795225](https://bugzilla.mozilla.org/show_bug.cgi?id=795225).

According to MDN, [pointer-events](https://developer.mozilla.org/en-US/docs/CSS/pointer-events) is not supported in all browsers. This is probably not a big issue, since the problem described in the bug seems to only affect the Firefox add-on.