The spec will probably change so that 350msec delay drops to 50msec.
XHR2 has been updated and it says 50ms.
Created attachment 355936 [details] [diff] [review] patch A testcase http://mozilla.pettay.fi/xhr_upload/xhr_upload_demo.html
Er, this is the test http://mozilla.pettay.fi/xhr_upload/xhr_upload_demo_timers.html (which may take *long* time to load because of some JS regression) I'll check if mochitest can handle such tests nowadays.
http://hg.mozilla.org/mozilla-central/rev/aeca8558250a Will commit to 1.9.1 soon.