For example, this extremely common crash...

https://crash-stats.mozilla.org/search/?signature=~RTCRtpTransceiver%3A%3AApplyCodecStats&date=%3E%3D2022-11-03T19%3A48%3A00.000Z&date=%3C2022-11-10T19%3A48%3A00.000Z&_facets=signature&_sort=-date&_columns=date&_columns=signature&_columns=product&_columns=version&_columns=build_id&_columns=platform#facet-signature

... does not show up in this search (for "webrtc" in topmost filenames) ...

https://crash-stats.mozilla.org/search/?topmost_filenames=~webrtc&date=%3E%3D2022-11-03T20%3A02%3A00.000Z&date=%3C2022-11-10T20%3A02%3A00.000Z&_facets=signature&_facets=process_type&_sort=-date&_columns=date&_columns=signature&_columns=product&_columns=version&_columns=build_id&_columns=platform#facet-signature

...however, it does show up in this search (for "xpcom/threads" in topmost filenames):

https://crash-stats.mozilla.org/search/?topmost_filenames=~xpcom%2Fthreads&date=%3E%3D2022-11-03T19%3A58%3A00.000Z&date=%3C2022-11-10T19%3A58%3A00.000Z&_facets=signature&_facets=process_type&_sort=-date&_columns=date&_columns=signature&_columns=product&_columns=version&_columns=build_id&_columns=platform#facet-signature

The topmost frame (in file "dom/media/webrtc/jsapi/RTCRtpTransceiver.cpp") is inlined, and can not be detected by the filter, whereas the first non-inlined frame (in "xpcom/threads/MozPromise.h") can be detected by the filter.

The topmost_filenames doesn't take inline functions into account. I'll toss it in the queue to fix.

willkg merged PR #6257: "bug 1800141: fix topmost_filenames" in 157d9dc.

I pushed this just now to production in bug #1803661.