Bug 18423 was apparently responsible for revision 1.43 of nsBrowserInstance.cpp which was the first time that EndDocumentLoad started using the channel's originalURI. Nobody thought to change StartDocumetnLoad to match, and this distinction has been propagated down the line in such bugs as 46200 (which moved the code from C++ to JS). However this causes a problem when restoring or opening a tab or window with a redirected URL such as an about: URL; in this case the underlying URL temporarily flashes up in the URL bar until the location change notification updates it with the correct URL.
Created attachment 408354 [details] [diff] [review] Proposed patch
Pushed changeset 3643ca91a6c6 to comm-central. Pushed changeset ca65c3600243 to releases/comm-1.9.1