FIX: Using k on Firefox to navigate up the topic list

Using k wouldn't always bring the topic in focus as you moved up the topic list
https://meta.discourse.org/t/topic-list-keyboard-shortcut-previous-k-does-not-scroll-properly-leaving-selected-item-hidden-firefox/20050
Merge pull request #2802 from cpradio/firefox-use-k-to-scroll-up

FIX: Firefox - Topic List Keyboard shortcut Previous(K) does not scroll properly leaving selected item hidden