We were trying to figure out why BenWa's Gecko Profiler UI extension doesn't work on my profile, and after a bit of debugging it boiled down to this code <http://mxr.mozilla.org/mozilla-central/source/toolkit/mozapps/extensions/XPIProvider.jsm#5767> throwing an exception when calling nsIOService::NewURI(). When I broke inside NewURI(), here's the aSpec parameter like this: (gdb) p aSpec $1 = (const nsACString_internal &) @0x11f7495f0: {mData = 0x1230da4c8 "[xpconnect wrapped nsIURI @ 0x11db10510 (native @ 0x15e5f4a08)]", mLength = 63, mFlags = 5} Which suggests to me that the target variable passed to newURI() is already a URI object, and the entire call to newURI() can be dropped. I tried doing that in my firefox build, and that breaks the add-on manager... So maybe target is sometimes a URL string and some other times a URI object? I'm not quite sure.

Per policy at https://wiki.mozilla.org/Bug_Triage/Projects/Bug_Handling/Bug_Husbandry#Inactive_Bugs. If this bug is not an enhancement request or a bug not present in a supported release of Firefox, then it may be reopened.