[bug 1087856] Add "Refresh Firefox" button

To test this edit an article and add the following somewhere in the content:
```
[[Button:refresh]]
```

You will also need to whitelist your local domain following the directions here: http://bedrock.readthedocs.org/en/latest/uitour.html#local-development

You should now see a "Refresh Firefox" button. Clicking on this will prompt you to reset Firefox.

N.B.: You will need Firefox >= 35

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