I think this is cleaner:

```
slimerjs = options.slimerjs or not have['phantomjs']
c_js =  [JSController(name, use_gecko=slimerjs) for name in js_testgroups]
```

Or possibly this is where we add  a `configure_js_controllers` function, like `configure_py_controllers`, and make `use_gecko` a method on JSController, like `add_xunit` and `add_coverage` on PyTestController.

Finally, I think the naming should be consistent in referring to either slimerjs or Gecko.