steps:
- bookmark the current page (in Chrome, you can drag the lock next to the url to the bookmarks bar)
- right-click the bookmark
- click Edit...
- change the url to the following (copy/paste)
javascript:(()=>{function t(e){e.body?.toggleAttribute("contenteditable");let n=e.getElementsByTagName("iframe");for(let o of n)try{t(o.contentWindow.document)}catch(c){}}t(document)})();