User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:57.0) Gecko/20100101 Firefox/57.0 Build ID: 20170805100334 Steps to reproduce: Switch between Default and other themes in Nightly. Could not reproduce this in Developer Edition. Tried in both normal and safe mode. Actual results: The theme did not fully apply. In the case of the persona theme, there was no change at all. When changing to Default from Dark or Light, there were noticeable differences, though it was still incorrect. Expected results: The theme should have changed to Default.