Fix protocol handler for mixed content blocking (#77)

The "floatnotes:blank" URL was treated as "mixed active content" and
therefore blocked if "security.mixed_content.block_active_content" was
set to true (the default). Using the URI_IS_LOCAL_RESOURCE protocol flag
solved the issue.
Add Danish localization
Add Japanese localization
Adapt to changes made in FF22.

Until we found a way to get favicon URLs synchronously, we only show the
default favicon in the note list.
Version 0.8.1