I browse with Firefox and 50% of the time, I am behind a proxy. The proxy firewall blocks certain sites including Facebook, Pinterest, and Twitter. I am unable to obtain a complete list of blocked sites and the list may grow daily.

Some legitimately unblocked websites (example: StackOverflow) may embed items (images, blocks of code, CSS, JavaScript) from blocked websites (example: user avatars on StackOverflow hosted on Twitter or Facebook). When these legitimate pages load, the firewall on the proxy throws a pop-up alert on the client for each individual item embedded from a blocked site.

These pop-ups are annoying and can be numerous. The pop-ups do not indicate which blocked site is causing the pop-up to appear.

I want to be able to load pages from these legitimate sites while simultaneously blocking or otherwise redirecting / intercepting the calls made from the browser to the blocked sites so requests to the blocked sites are not made at all, or at least directed to a harmless (localhost?), yet invalid site. I am not looking to circumvent the blocking mechanism; I am looking to prevent the calls from a browsed unblocked page to embed from blocked sites.

I am not sure where to start. Online searches against what I'm looking for have failed (granted, maybe I'm not using the correct terminology), and I've tried altering the hosts file to direct certain sites to, but that does not appear to be working (it is possible I am not listing all the proper sites).

Are there any FireFox plug-ins or other recommendations to do this?

Without having to scrounge through the source of the loaded page,

  1. where do I look to obtain a list of the sites a webpage I've browsed to is trying to embed/call? I cannot obtain this list from the pop-up and having the list might solve the majority of my problems.
  2. how do I prevent these blocked sites from being embedded by the page I'm calling, or otherwise intercept the calls to the blocked sites? Suggestions for Firefox plug-ins and how to configure them appropriately or other alterations are appreciated.
  3. preferably a way to easily enable and disable this functionality on demand.

I can't speak for Firefox directly, but the Chrome developer tools will present you with a list of every web request made by a page while it loads, and I believe Firefox's dev tools will do the same.

As to stopping the requests, AdBlockPlus for Firefox and Chrome should be able to stop the browser from making the requests. Doing a global block for facebook.com/* or *.facebook.com/* should result in embedded content from facebook not loading.

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