Arrow keys in the editor started acting a little strange in Firefox a few versions ago. The up and down arrows sometimes require an extra press to get past paragraphs.
Create a new default Firefox profile. I was using Ubuntu 20.04.
firefox --new-instance --profile $(mktemp -d) &
Start a new forum post. Make a few paragraphs. Push the up and down arrow keys and watch for keypresses that don’t move the cursor.
Also, I’m not sure if this is a bug or if it was intended, but the tab index changed in the editor. Previously you could type a message, press tab and then you would be on the submit button, but now it takes 2 tab presses.
I can get used to the change, but I thought it might be a bug. If it was an accident, one tab is more convenient for keyboard-oriented users and will prevent them from having to relearn the muscle memory. I’m not sure if that one is a bug, so I’m just mentioning it in passing here.