User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:55.0) Gecko/20100101 Firefox/55.0 Build ID: 20170816210634 Steps to reproduce: Tried to get title of a given URL page from within the background page. Attempts were done with iframes and ajax, but no single solution could work consistently for all websites. They were suggested on https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Comparison_with_the_Add-on_SDK#JavaScript_APIs as a page-worker replacement Code: https://github.com/LoveIsGrief/links-for-later/blob/links-for-later-4/webextension/index.js#L117 Actual results: webrequests and webrequestsBlocking had to be used to block or modify certain headers in order to allow CORS. Depending on the website iframes didn't work (github) or ajax didn't work (reddit) due to primarly 2 reasons: - CORS not completely blocked - anti tracking activated and site not loaded (reddit) I'm sure I'll stumble upon more, but that's what I ran into Expected results: It should've been possible to simply get the title without additional rights (webrequests, webrequestsBlocking) or a visible page (tabs, windows). So either page-workers are needed or invisible tabs (which are page-workers AFAIK). page-worker API: https://developer.mozilla.org/en-US/Add-ons/SDK/High-Level_APIs/page-worker