Is it only on Mac it shows the actual status codes on the network tab? On Windows i have to hover the little icon in the first column, which is really annoying when I'm trying to figure out if my caching is working correctly.
Sounds like your windows copy of firefox might be the main release channel. The numeric status codes have been in since 30 (currently Beta). You can hop on Aurora (or Beta, or Nightly, but Aurora is generally best for web devs), or just wait about 6 weeks for the next uplift.
https://bugzilla.mozilla.org/show_bug.cgi?id=972054