[CMD] + [OPT] + [ i ] (Mac)
[CTRL] + [SHIFT] + [ i ] (Windows)
The Rules view lists all the rules that apply to the selected element, ordered from most-specific to least-specific:
The Layout Panel shows the Box Model and how it is applied to the selected element.
This panel shows the calculated value that each CSS property has for the selected element:
This panel shows all CSS that you have changed in browser.
Allows you to view and edit associated stylesheets as well as create new stylesheets from scratch.
Style Sheet Pane
The Grid Inspector allows you to examine CSS Grid Layouts using the Firefox DevTools, discover grids present on a page, examine and modify them, debug layout issues, and more.
The Flexbox Inspector allows you to examine CSS Flexbox Layouts using the Firefox DevTools, discover flex containers on a page, examine and modify them, debug layout issues, and more.