Removing black boxes in URL bar on Firefox on Lubuntu

After a fresh install of Lubuntu 14.04 this week (yes, I know 14.10 is out, but I'm a LTS kind of guy) on an old Samsung Sens X05 laptop, everything went well except for (1) typing in Korean (which was remedied by my old method here) and (2) some strange black boxes that blocked out the text in the URL bar in Firefox.

Luckily it was a very easy fix, following this suggestion:
  1. Go to about:config
  2. Search for the "gfx.xrender.enabled" entry
  3. Toggle to "false"
  4. Restart Firefox

Ah, that fresh, clean, new-install feeling...