https://support.mozilla.org/en-US/kb/keyboard-shortcuts-perform-firefox-tasks-quickly Tools Responsive Design View Ctrl + Shift + M Bing Search https://www.bing.com/search?q=firefox%20%2Bresponsive%20%2Bdesign&pc=MOZI Enabling and disabling Edit There are three ways to enable Responsive Design View mode: Select "Responsive Design View" from the Web Developer submenu in the Firefox Menu (or Tools menu if you display the menu bar or are on OS X) Press the "Responsive Design View" button in the Toolbox's toolbar Press Ctrl + Shift + M, (or Cmd + Opt + M on OS X)