Can't drag scroll bar for virtual scroll region in Firefox

#### Reproduction

Use example page https://material.angular.io/cdk/scrolling/examples

Steps to reproduce:
1-open the example page in Firefox
2-try to drag the scrollbar handle

#### Expected Behavior

Expected that drag handle moves when mouse moving

#### Actual Behavior

scrollbar doesn't move

#### Environment

- CDK/Material: 10.2.7/9.2.4/11.2.1
- Browser(s): Browser(s): FireFox 85.0.2 (64-bit)
- Operating System : Windows 10

Start by reproducing the issue on the CDK scrolling examples page in Firefox 85 on Windows 10, then trace the virtual scroll region entry point responsible for scrollbar dragging. Done means the scrollbar handle moves while dragging in Firefox without regressing the documented scrolling behavior.

Written by the indexing model from the issue text.