Update DM Strings r=kaze, arcturus

It seems that previous revert based on:
https://tbpl.mozilla.org/php/getParsedLog.php?id=33755141&tree=B2g-Inbound

was related with:
https://github.com/mozilla-b2g/gaia/pull/15356/files#diff-0cc6cad7bebc06da022e6c5a59f2cfd8R103

Now this line has been removed. Uploading the patch rebased!