use Firefox latest stable (v33.1.1)

PeterDaveHello · pde · commit 108527aadacf · 2014-11-27T15:08:16.000+11:00
diff --git a/.travis.yml b/.travis.yml
@@ -5,8 +5,7 @@ language: python
 python:
   - "2.7"
 addons:
-  # Firefox 31 doesn't seem to be available on travis-ci.org yet.
-  firefox: "30.0"
+  firefox: "33.1.1"
 install:
   - sudo apt-get -qq install libxml2-dev libxslt-dev python-dev
   - pip install -r requirements.txt
