Adblock Plus and (a little) more: Displaying web content in an extension - without security issues

"Over the last few years I reported a bunch of security vulnerabilities in various extensions and by far the most common issue was: “Extension Foo allows execution of remote code in privileged context”. Typically, an RSS reader extension would take the content of the RSS feed (HTML code), format it nicely and insert into the extension window. The issue that is overlooked here is that the RSS feed could contain some JavaScript code and it would then execute with the privileges of the extension — meaning for example that it would get full access to the browser (cookies, history etc) and to user’s files. pdp discovered a similar issue in the Firebug extension that uses an HTML-based templating system and forgot to sanitize some input received from the webpage."