I've been using Adblock Plus to block ads in feeds rendered using the Sage extension. No problem, using Sage 1.3 which generates the page and opens it with a file://... URL.
However, I recently installed a nightly build of Sage 1.4, which now uses chrome URLs (chrome://sage/content/feedsummary.html?uri=...) Adblock Plus does not work on these pages and when I open the blockable items view, it informs me that it isn't a remote page.