This code: https://github.com/mozilla/gecko-dev/blob/master/devtools/server/actors/script.js#L1966-L1972 We had a regression that made that `unsafeSynchronize` not run, and we never noticed. Top-level sourcemapped breakpoints didn't work sometimes then. This is fixed in bug 1177329 but we still have no tests for it. We should write a test that fails when we hit whatever condition that that code solves. I'm not familiar with the problem enough to write a test yet.