After the latest NoScript update (https://noscript.net/?ver=2.6.9.29&prev=2.6.9.27), needed to allow ajax.googleapis.com to be able to do anything on the site (upvoting, commenting, etc).
Not sure though whether this is due to said update or a concurrent change on SX.
The above applies to Firefox (and NoScript) ...
Further reading:
https://developers.google.com/speed/libraries/
The Google Hosted Libraries is a stable, reliable, high-speed, globally available content distribution network for the most popular, open-source JavaScript libraries.
Google works directly with the key stakeholders for each library effort and accepts the latest versions as they are released.
Libraries
To load a hosted library, copy and paste the HTML snippet for that library (shown below) in your web page. For instance, to load jQuery, embed the
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>snippet in your web page.
http://www.w3schools.com/jquery/jquery_get_started.asp
One big advantage of using the hosted jQuery from Google or Microsoft:
Many users already have downloaded jQuery from Google or Microsoft when visiting another site. As a result, it will be loaded from cache when they visit your site, which leads to faster loading time. Also, most CDN's will make sure that once a user requests a file from it, it will be served from the server closest to them, which also leads to faster loading time.
http://encosia.com/3-reasons-why-you-should-let-google-host-jquery-for-you/
(...) I urge you to use the Google HostedLibraries content delivery network to serve jQuery to your users directly from Google’s network of datacenters. Doing so has several advantages over hosting jQuery on your server(s): decreased latency, increased parallelism, and better caching.