Hi, The sidebar always remains white regardless of the theme that you have enabled. The people who answer questions here, for the most part, are other Firefox users volunteering their time (like me), not Mozilla employees or Firefox developers. If you want to leave feedback for Firefox developers, you can go to the Firefox ''Help'' menu and select ''Submit Feedback...'' or use [https://qsurvey.mozilla.com/s3/FirefoxInput/ this link]. Your feedback gets collected by a team of people who read it and gather data about the most common issues.