[staktrace]

Try looking at about:support to see if there are any third-party modules (antivirus etc. loaded). That has been a cause of problems like this in the past. More likely on Windows and I saw you're running macOS, but worth a shot.

[commoner]

It's worth a try, though Firefox has discontinued support for NPAPI plugins since version 52 (March 2017)⋮ https://support.mozilla.org/en-US/kb/npapi-plugins

The only plugins in the Plugins section of about:addons should be the OpenH264 plugin and the Widevine plugin (only if DRM is enabled). Both can be disabled there.