A couple of front dev questions in Firefox?

Question

Browsers

Hello everyone, I moved after Chrome and there are two questions:
1) Is there a Page ruller in the fox? For example, measure the distance from button to button?
2) Chrome has the ability to scale the device-mode. That is, you can even look at a 4k site. Is there such a thing in fox?
3) Is there any difference for us, coder-programmers, between production and dev versions of fox?
Thanks

Answer 1

1. Moskus has already answered. I'll add one more thing useful for stretching meshes.
2. Firstly, there is a built-in Responsive Design Mode mechanism . Secondly, there are extensions ( 1 ) ( 2 ) ( 3 ) for old foxes or for those who are not looking for easy ways.
3. The dev version has significant differences for the developers of the extensions of the fox itself. From the point of view of web development, these differences play almost no role.