I'm using epiphany-browser v2.30.2 to listen to a midi from a site when it prompted me to install the gstreamer plugin. After looking at the crash it seems the problem is in libwildmidi, in either a realloc or free. While it appears the version of wildmidi packaged with that plugin is v0.2.2, the bug may be in more recent revisions since the page/browser combination are a bit uncommon.
I was able to reproduce the crash multiple times:
Click play, click stop, click play, get crash.