Anarchist Framer allows you to strip X-Frame-Options from frames loaded on pages you whitelist. This was created for Comic Rocket's reader (*://www.comic-rocket.com/read/*), but it should be useful elsewhere.
Warning: You can make this add-on globally strip headers from every site by specifying *. You probably don't want to do this because it will bypass valid security mitigations that use X-Frame-Options. Only whitelist a site if you're sure this won't result in you getting phished. (This is fine for Comic Rocket, as they aren't going to be asking for personal information in the reader or framing my bank site, but please do evaluate all other sites you decide to whitelist.)
