Newer versions of Firefox use styleSheetsActor

This is a blocking bug for the execution of the tool
fetchSource is now getText

Blocking issue, Sublime gets frozen because receive() waits forever
#3 there is no need to receive
Merge pull request #2 from nicolagreco/patch-1

Newer versions of Firefox use styleSheetsActor
Merge pull request #3 from nicolagreco/patch-2

fetchSource is now getText