Sorry to hear about the crashes and thank you for the crash report ID.

It indicates that the crash occurs in "MySpeed" which appears to be a program from Enounce that interacts with Firefox and other browsers.

Have you been using that software with Firefox for some time now? I don't see any new issues posted on their support page related to Firefox 55: http://www.enounce.com/support-known-issues

Looking at the article for Firefox 52, you may want to try disabling MySpeed integration with "Firefox's Plugin Container" to see whether that helps: http://www.enounce.com/FirefoxForMacSandboxInfo

I just started using myspeed, but plenty of my classmates use it with no problem. Even with changing the sandbox level to 0, firefox still won't work. I have to completely inactivate myspeed for firefox to work, which defeats the purpose of having it.

Did you quit Firefox and restart it after making the settings change?

If they still do not run together, could I suggest contacting the company's tech support to see whether they know of a new Firefox issue since their last update?

Yes, no success with that. I gave up on firefox and wiped it from my computer. Myspeed works with Opera, so I'll just watch our out-of-class lectures through Opera instead of Firefox. At some point, it's just not worth the hassle of trying to make firefox cooperate when we run on a pretty tight schedule. But thank you for your help!!