They should appear on about:crashes. But: bug 1655323 didn't generate any crash reports for me, the tab just became black. Therefore I assume the crash report might not have been about WebGL becoming black.
Bug 1660675 Comment 6 Edit History
Note: The actual edited comment in the bug view page will always show the original commenter’s name and original timestamp.
They should appear on about:crashes. But: bug 1655323 didn't generate any crash reports for me, WebGL just became black. Therefore I assume the crash report might not have been about WebGL becoming black.