Firefox does not have a button to reset the developer tools like Chrome has had for years, that is very important for some developers, if not in the standard version, at least in the developer version.
They most likely mean the “Restore defaults and reload” button.
This button can be found in Chrome by opening the developer tools (Ctrl + Shift + I), clicking on the cog icon to go to the settings (or just pressing F1) and scrolling down to the bottom of the “Preferences” tab.