Yea, realized I wrote mxr instead of dxr but couldn't edit before my post was accepted.

I do find it weird that config specs are linking to source code, instead of explicitly giving the options, but the information seems to still be correct.

LXR & MXR replaced by DXR
http://mxr.mozilla.org/

nsDOMEvent.cpp
http://dxr.mozilla.org/mozilla/source/content/events/src/nsDOMEvent.cpp

FYI, that file is from a really old build.

version.txt
http://dxr.mozilla.org/mozilla/source/browser/config/version.txt

I noticed a broken link in a kb [url=http://kb.mozillazine.org/Dom.popup_allowed_events]article[/url].
It's linking to http://lxr.mozilla.org/mozilla/source/content/events/src/nsDOMEvent.cpp but I'm assuming the subdomain should be mxr, as the link is currently broken.
I don't have modification permissions to modify it myself.