I was watching a tutorial video made on the web recently，Noticed that the instructor used a certain tool，You can drag the mouse cursor on the browser screen，The length and width of the drag appear instantly，This way when you want to know the size of the page element，Very convenient。After not finding the relevant function in Firefox，Then go to the plugin component to start，After a goo，In addition to related plugins，It turns out that Firefox is built-in，I just have to manually turn it on。
◎ Press F12 to open "Web Developer Tools"。
◎ Click「…"-"Setting"，Find the "Part of the measurement page" under the "Available Toolbox Buttons" category and check。
◎ Then you can click on "…"I see a ruler pattern on the left。
◎ After activation，Can be measured on the screen。
【Examination link】
- Rulers – Firefox Developer Tools | MDN
