• Implement cross-origin wrappers #2382 - cross-origin window.parent
• The offsetWidth of a span element is 0. #12939 / Erroneous result for offsetHeight on Google Docs #13944 - offsetHeight
• Implement Location.replace #13413 - location.replace()
• Implement Document.open() and Document.close() #14591 - document.open/document.close
• Layout assertion visiting google accounts help page #14783 - Panic in layout code
• Calling matchMedia during a MQL change event will panic #14967 - Panic during Window.matchMedia
• TransitionEnd event can include nodes that have been GCed #14972 - JS engine crash when using animations
• Determine why the toolbar collapses when viewing a document in Google Docs #15500 - Toolbar mysteriously collapses
• Locked::read_with called with a guard from an unrelated SharedRwLock #16097 - Panic in style/shared_lock.rs
• Implement History State #20638 - History.replaceState

The following issues are not proven to be directly blocking basic usage but are known to be used by Google Docs:

• Implement IndexedDB. #6963 Implement IndexedDB
• Implement support for the resolution media query #16101 Implement support for the resolution media query
• Implement element.innerText #16107 Implement element.innerText