Currently mozilla_sampler_get_backtrace() does not capture a stack if either: (a) We're not currently profiling; or (b) The profiler is in privacy mode. For the purposes of mozilla_sampler_get_backtrace(), these restrictions are too conservative. In particular, we should still be able to capture a stack using mozilla_sampler_get_backtrace() even if the profiler is initialized but not currently running. In the case of (b), we can still capture a backtrace as long as we restrict ourselves to the C++ stack.

I think we can kill (b). Currently in the platform code we already keep URLs in memory and we already have a system for grabbing backtraces. It's up the user of the backtrace to deal with private browsing correctly. Fixing a) would be great.