Having an already-cancelled channel fail synchronously when AsyncOpen is called has the bad effect that if the channel is a redirect, it vetoes the redirect (as opposed to continuing with the redirect but cancelling the resulting channel, as calling Cancel after AsyncOpen does). Cancel should have the same semantics for redirects before/after AsyncOpen. (see bug 766210 for example). The only reason I added the sync failure in bug 584863 is it resulted in fewer IPDL messages in e10s (but only for the early cancel case: not worth optimizing).

Try build at https://tbpl.mozilla.org/?tree=Try&rev=59d4d4b8ed5f

Try looks fine.

Comment on attachment 641628 [details] [diff] [review] v1 Review of attachment 641628 [details] [diff] [review]: ----------------------------------------------------------------- r=honzab, disavowing from consequences :)