It’s actually when I try to access the widgets page in my account (https://twitter.com/settings/widgets) that I’m seeing the error.
Chrome: Version 43.0.2357.124
Safari: Version 8.0.6
I’ve noticed that my embedded widgets seem to be working again now (widget-id=“586174233371398145” for example), but I can’t access the widgets page to set up new ones or amend widgets.