Add support for detecting firefox versions 29 - 32

Adds some more feature detection code.

#### Verification

Make sure the os.js script works on each of the following Firefox versions. I usually do this by just adding the line `console.log(os_detect.getVersion())` to the bottom, and then copy and paste the whole thing into Firefox's Tools->Developer->Web Console.

- [ ] Firefox 27
- [ ] Firefox 28
- [ ] Firefox 29
- [ ] Firefox 30
- [ ] Firefox 31
- [x] Firefox 32