Release 3.1.0 Features: * userChrome/popups.css: Hide some context menu items (MR 24) Fixes: * mobile-config-prefs.js: fix titlebar for plamo (MR 23) Other: * Makefile: remove unused variables (MR 21) * README: add resource "How to use the Firefox Browser Toolbox" (MR 22) * treewide: change license to MPL-2.0 * treewide: bump copyright to 2022