Since about:support was written under browser/, it has a fair number of expectations about living there, and as bug 518607 comment 2 points out, we should reduce the dependencies (that aren't already certain for any toolkit app) and then document the rest of them in a comment, so that potential consumer apps don't need to read through every scrap of the JS to know that they need to provide an app.support.baseURL pref, and whatever else we leave as a requirement.

I just built SM with the new code. It reports that Cc["@mozilla.org/fuel/application;1"] is undefined (aboutSupport.js line 51) which doesn't come as a surprise since SM has SMILE instead of FUEL. I guess the same is true for TB (s/SMILE/STEEL/).

Oops, the patch in bug 518607 removed that bit, but I must have done the patch in bug 518989 by copy-pasting from the browser/ version of the file rather than the toolkit/ one. Fixed in http://hg.mozilla.org/mozilla-central/rev/2ef9c0ee3a71

about:support lives in toolkit now. I think the only dependency on Firefox, if it can be called that, is that the list of whitelisted preferences contains browser.* preferences. The other issues in bug 518607 comment 2 are moot now. There's no way to modify that whitelist without modifying Troubleshoot.jsm, but the same is true for all the data providers in Troubleshoot.jsm, which other apps could presumably modify as they see fit. If we want pluggable data providers so that Troubleshoot.jsm doesn't need to be modified, then that's probably better as a new bug. So it seems like this bug is satisfied.