Webpage size shouldn’t depend on browser chrome
Tor Browser 8.0.3 (64 bits, Windows 10) has a default window size of 1002 × 995 pixels.
When enabling the Bookmarks Toolbar (i.e. making it always visible), the browser window stays the same size, thus reducing the size of the webpage (and helping fingerprinting).
This also happens with the Menu Toolbar (and is arguably worse for fingerprinting, because the resize happens interactively on keypress, e.g. Alt + F) and the Bookmarks sidebar.
To keep the webpages the same size for all the users, I propose that enabling toolbars and sidebars also extend the size of the browser window by an appropriate amount.