Hmm, I can't tell what causes this crash. It doesn't seem unique to beta/developer; it has been detected for several past versions. But everything was fine for you with Firefox 66?

Thank you for replying so quickly!

I have downloaded and unpacked Firefox Developer Edition 67.0.b1 archive (so, the same version number that's in the crash report) over the one that was crashing and it has solved the issue. This leads me to believe it might have been a borked auto-update.