In Slack, when I'm browsing a channel, if I press PageUp/PageDown, the channel content scrolls smoothly, i.e. the content moves one screen line at a time and it takes about one second to perform the operation. Strangely, I only have this problem with PageUp/PageDown: other methods of scrolling, such as Up/Down, the mouse wheel or clicking on the scroll bar to scroll by one page at a time work instantly.
I have smooth scrolling disabled in my browser. I tried with both Firefox and Chrome.
How do I turn off Slack's smooth scrolling?