When working on bug 1320402 ehsan found that xml-fetcher.js may not be test[1]. This bug is used to investigate if that is an untest path and add a testcase for it. [1] https://bugzilla.mozilla.org/show_bug.cgi?id=1320402#c20

I think, when safe browsing code was moved from extension to be a part of Firefox, some parts are not being used (dead code probably). For example xml-fetcher.js, trtable.js (or preference.js). I don't see the Fetcher is being used currently, am I missing anywhere? (gcp could be have the better historical view of safe browsing code)

That's correct. Also most stuff in content/moz is no longer used. If you want to have a go at just removing them be my guest!