Some browsers have built in support to test websites across different device widths/heights. 

Firefox refers to it as their "Responsive Design Mode" and Google Chrome refers to it as "Device Mode".

With this mode enabled, a user can simulate viewing a website on a mobile device or tablet.

• For Google Chrome, refer to:  https://developers.google.com/web/tools/chrome-devtools/device-mode/
• For Firefox, refer to:  https://developer.mozilla.org/en-US/docs/Tools/Responsive_Design_Mode