We've started seeing issues recently with the comment dialog in both

Chrome and Firefox when attempting to scroll the text field. On Chrome,

any attempt at scrolling the text area would also result in the page

being scrolled. On Firefox, scrolling might not even work at all.
This was in part caused by some old overflow style rules we had for

the scroll container, which at some point was necessary to fix some

styling issues, but these days interacts poorly with modern scrolling

behavior.
Removing these rules and adding overscroll-behavior-y: none fixes

this. This new property tells browsers not to continue scrolling when an

inner scrolling element is scrolled to the very top or very bottom. It

also seems to correct some quirky scrolling issue currently specific to

Chrome, which was causing both the page and CodeMirror to scroll

simultaneously.

Tested scrolling in the comment dialog and text fields in Chrome, Firefox,

and Safari.
My version of Safari is a bit old, and does not support overscroll-behavior,

but scrolling still works fine until the boundary of the scroll range is hit.