Apply Mozilla patches

Apply all relevant patches on Mozilla's master branch that were committed after creating this fork at 3e9be676.

The latest commits on Mozilla's master branch also implement download reporting and download tokens among other things. Do not include these to remain compatible with the last public version and ffsend.

Commits to apply: mozilla-master..3e9be676413a6e1baaf6a354c180e91899d10bec