CSS ::-moz-selection not working in Firefox (Webpage)

This program has a help request regarding how ::-moz-selection is not working in the KA sandbox in Firefox. However, when the code is used in a .html file on my computer, it works in Firefox.

Here is a sample of code which does not work, and works in Firefox.

`

Project: Blog

::-moz-selection {
color: red;
background: yellow;
}

Text to highlight for testing.

`

Issue was first encountered at:

https://www.khanacademy.org/computer-programming/project-blog/6474254003339264?qa_expand_key=ag5zfmtoYW4tYWNhZGVteXJpCxIIVXNlckRhdGEiRnVzZXJfaWRfa2V5X2h0dHA6Ly9pZC5raGFuYWNhZGVteS5vcmcvYjQ0YzllYTA0NGRlNDFjZWIwZTE4NGZmMmZkNTI4MWYMCxIIRmVlZGJhY2sYgICAgO2tkgoM

Reproduce the linked KA sandbox example in Firefox and compare its selection behavior with the standalone HTML sample in the issue. Trace how the sandbox renders and scopes webpage CSS; done means ::-moz-selection styling works in the sandbox as it does in the standalone page.

Written by the indexing model from the issue text.