Bugzilla

We collected enough data to know that we seem to not wait for whatever is ongoing in the BitsCommander thread while [creating a COM object](https://hg.mozilla.org/mozilla-central/annotate/c47b3b28fb48c01c33585b46650249b182cabe00/third_party/rust/comedy/src/com.rs#l232).

To reproduce the failure locally you could add a very long sleep before [instantiating the BackgroundCopyManager](https://searchfox.org/mozilla-central/rev/2e7374599f4020d0490ec8c5e877c179c9e153c9/toolkit/components/bitsdownload/bits_client/bits/src/lib.rs#120-123) and somehow trigger that code path (I do not know under what conditions this COM instantiation is activated). The stack [from the BitsCommander thread](https://crash-stats.mozilla.org/report/index/0163ad99-90b3-4580-bd9e-4c95d0240425#allthreads) on one of those crashes might give you some hint on what to activate, too. IIUC it all starts with `StartDownloadTask`, bit I do not know how to force it to run (some of the tests might know?).

We collected enough data to know that we seem to not wait for whatever is ongoing in the BitsCommander thread while [creating a COM object](https://hg.mozilla.org/mozilla-central/annotate/c47b3b28fb48c01c33585b46650249b182cabe00/third_party/rust/comedy/src/com.rs#l232).

To reproduce the failure locally you could add a very long sleep before [instantiating the BackgroundCopyManager](https://searchfox.org/mozilla-central/rev/2e7374599f4020d0490ec8c5e877c179c9e153c9/toolkit/components/bitsdownload/bits_client/bits/src/lib.rs#120-123) and somehow trigger that code path (I do not know under what conditions this COM instantiation is activated). The stack [from the BitsCommander thread](https://crash-stats.mozilla.org/report/index/0163ad99-90b3-4580-bd9e-4c95d0240425#allthreads) on one of those crashes might give you some hint on what to activate, too. IIUC it all starts with `StartDownloadTask`, but I do not know how to force it to run (some of the tests might know?).