Add new question:"What are these grey bars on resized Tor Browser window?"

In Tor Browser 9, "when user resizes the window, then grey bars are around the window from inside", see trac#32149.

This is a feature called letterboxing, and its purpose is to defend against fingerprinting of your screen dimensions.

More information: ​https://www.zdnet.com/article/firefox-to-add-tor-browser-anti-fingerprinting-technique-called-letterboxing/.