Thanks for the reminder! I'd read about this a long time ago, wasn't sure it was as yet widely supported.

My immediate response was to separate the permalink into a pair of permalinks, one for the editor and one for pure playback.

https://github.com/judell/av/commit/a4b3ee5102048a7ca87e7a4bedd8537f45fae754

What I'm seeing when I try the playback links on, say,

http://ia601503.us.archive.org/2/items/180104OSPODCASTMarkBlyth/180104-OS-PODCAST-MarkBlyth.mp3#t=2696,2821

http://ia601503.us.archive.org/2/items/180104OSPODCASTMarkBlyth/180104-OS-PODCAST-MarkBlyth.mp3#t=2696,2821

Chrome: All good
Edge: No interest in #t=start,stop
Firefox: Respects #t=start,stop but no sound (I've read about MP3 playback issues in FF)
Safari: Don't have a Mac nowadays

Curious to know how that tallies with your observations.