View Rulers in Firefox – Horizontal and Vertical

The most useful tool is a ruler, Firefox has a ruler to display both directions. To view the ruler just press the menu button and navigate to Developer Toolbar via Developer option or menu items. Shortcut key Shift + F2. The toolbar will be appearing at the bottom of the page. Just type rulers keywords and press Enter to enjoy the ruler functionality with pixel units on the page. Click the Toolbox Options and check the Toggle rulers for the page checkbox under the Available Toolbox Buttons to make it appear on your developer tools window.