Any site that uses Adobe Flash for video or audio causes the tab that it's in to immediately crash. I've reinstalled Flash, Firefox, and made sure there are no pending updates for anything. I installed Chromium browser (blech!) and it works without issue, so I'm pretty sure this is a Firefox related issue. I'm currently trying to get support from Mozilla. This is why I don't really like installing things immediately when they just come out. Many times, there are undiscovered bugs. The version of this OS (Lubuntu 18.04) just came a few weeks ago, and this version of Firefox (60.0) came out a week or so ago. I guess it never hurts to have two browsers installed. I haven't been real thrilled with Firefox since Quantum came out, but I don't want to switch to something else and give up some of my addons.