Can't scroll with PgUp/PgDown or arrow keys

[e00E]

Describe the bug

Just tried this in Firefox and Chrome on app.cinny.in. I can scroll with the mouse wheel or by dragging the (barely visible) scroll bar but not with the keyboard keys.

This is an important usability problem for me.

Reproduction

Go into any chat and try to scroll.

Expected behavior

No response

Platform and versions

Current releases of Firefox and Chrome on Linux.

Additional context

No response