How can I simulate mobile devices and debug in Firefox Browser? [closed]

You can use tools own browser (Firefox, IE, Chrome…) to debug your JavaScript.

As for resizing, Firefox/Chrome has own resources accessible via Ctrl + Shift + I OR F12. Going tab “style editor” and clicking “adaptive/responsive design” icon.

Old Firefox versions

New Firefox/Firebug

Chrome

*Another way is to install an addon like “Web Developer”