Feature/issue 165

Adds functionality that allows the user to whitelist certain potential trackers which need to be whitelisted to work. E.G. Youtube comments. This feature is already present in the chrome version but this would add it to the firefox version. CC @jsha for review. 
I'll not be a stickler about one-line if statements in general, but I think this one is long enough that it makes sense to put the return on its own line.