Background image responsive issues

[W3ap0n-X]

Site custom background images are not resizing properly on smaller devices.

To Reproduce
Steps to reproduce the behavior:

1. Create a page with enough content to require scrolling and any contact form or input element
2. Visit the page with a mobile device
3. Scroll down to the bottom of the page and immediately scroll up to the top and immediately back down to see the void left by the URL address bar.
4. Click your input/contact form and when the keyboard shows scroll down to see the void.

Expected behavior
Background image should adjust to fit device size on all device types

Screenshots

Additional context
Issue seems to be more prevalent on Firefox but still happens on Chrome