Rename .xul to .xhtml
Firefox did a mass rename of all .xul files to .xhtml in https://bugzilla.mozilla.org/show_bug.cgi?id=1579952. We need to do the same in torbutton and tor-launcher, as well as in several Tor Browser patches that involve UI.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information