I don't think you can copyright lists of publicly available information (iirc there was some case with phone numbers before).
That being said, they also stole code...
> For Zeidenberg's argument, the circuit court assumed that a database collecting the contents of one or more telephone directories was equally a collection of facts that could not be copyrighted. Thus, Zeidenberg's copyright argument was valid.[1] However, this did not lead to a victory for Zeidenberg, because the circuit court held that copyright law does not preempt contract law. Since ProCD had made the investments in its business and its specific SelectPhone product, it could require customers to agree to its terms on how to use the product, including a prohibition on copying the information therein regardless of copyright protections.
A similar example would be using a GPLv3 licensed JavaScript library in a website. What it implies to other HTML/JS/CSS code is controversial [0]. The FSF actually believed that they should not be "infected" [1], and the legal implications may need to be tested in court.
I don't think chrome extensions can be modified by the user; there's probably some integrity check. So to be GPL compliant they need to publish source files to rebuild the extension?