Slow scroll in the custom filter list using Firefox

Environment

• OS version: Ubuntu 18.04
• Browser version: Firefox 67.0.4
• Extension version: UI release 2019-1 [*]
  [*] Issue still appears on release 2019-4

Steps to reproduce

1. Open Advanced tab in desktop settings page
2. Go to My Filter List section and scroll down the list

Observed behavior

Scrolling is too slow, with a displacement of 3px per event.

Expected behavior

Scrolling should be faster, around 3 lines.

Suggested solution

As per https://gitlab.com/eyeo/adblockplus/abpui/adblockplusui/-/merge_requests/326#note_192490298, because of spec ambiguity, we decided that the definition of line height will be same as the height of the table row which will make Firefox users scroll 3 rows per event.