Horizontal scrolling of search results doesn't work in Firefox

Created by: mrnugget

• Sourcegraph version: sourcegraph.com
• Platform information: macOS, Firefox 73.0.1 (64-bit)

Steps to reproduce:

1. Go to https://sourcegraph.com/search?q=repo:%5Egithub%5C.com/papers-we-love/papers-we-love%24+compiler&patternType=literal
2. Resize browser window so that the search results show a horizontal scrolling bar
3. Try to scroll to the right on a search result

Expected behavior:

Scrolled to the right

Actual behavior:

Scroll bar is "draggable". See GIF:

(Feel free to re-assign/un-assign etc.)