Fuzz doesn't detect updates to the DOM in Firefox

[msporny]

Fuzzbot detects new triples when the document is loaded, in other words, when Javascript modifies the DOM, the document isn't re-parsed for new triples.

We might need a trigger to re-parse the triples once Javascript updates the page or the DOM changes. Currently we use the following call to retrieve the DOM contents:

serializer.serializeToString(gBrowser.selectedBrowser.contentDocument);

We run this when the 'load' or 'TabSelect?' event is fired via the UI. We should also do it when the DOM changes (waiting at least 3 seconds between calls to ensure that the UI isn't overloaded with triple generation).