And now the Slashdot issue is also fixed. Slashdot includes an iframe in their RSS feed that embeds their comment section, but Slashdot’s server blocks it from loading on any other site (they set X-Frame-Options to same-origin only). So it was just rendering as an empty broken box. I’m now stripping iframes from feeds that don’t allow cross-origin embedding while still keeping ones that work, like YouTube and Vimeo embeds.