One interesting change we made with SVG external document references is that the notificationCallbacks of a loadgroup are no longer necessarily something you can get a docshell from. I think this was already the case for images, but it will now generally be true for all external SVG resources and everything loaded from such documents. The reason for setting it up this way was to make sure people don't by accident treat an external resource load as being a load in the display document. That said, the load is of course associated with the display document...
So the question is whether there are extensions that rely on getting a docshell or some such from the notification callbacks, and if so what they need it for and what they'd expect to get for the external resource documents. I have no idea how to find this information, unfortunately, so I welcome any pointers.
The hgweb annotation output on hg.mozilla.org is painfully slow. On large files it's two orders of magnitude slower than our old Bonsai output.
The upshot is that the template for the annotation output needs to be changed (HTML coding plus a bit of Python, I assume) to output HTML that doesn't require O(N^2) behavior to render. Sadly, I'm a bit swamped for time to work on this right now, but if someone wants a way to seriously help out Gecko development without touching C++ code, this is it!
David Mandelin's blog post about one of the sunspider subtests is chock-full of fun information on regexps. It also highlights some more perils of writing performance tests, especially when there are optional features involved, or when the tests don't do a good job of testing whether the behavior is correct in addition to being fast.