https://html.spec.whatwg.org/multipage/dynamic-markup-insertion.html#document-open-steps step 2 checks for the document being an active document. Then step 10 runs arbitrary script, after which the document might not be active, the browsing context may not exist, etc. What should happen in this situation? Should the passed-in string still be parsed?

In Gecko I'm likely to add another active document check after step 10 and return document immediately if that fails, without doing any parsing.