Hi JGunn, this is the first I've heard of Jupyter Notebook so I thought I would check out a demo from their site. However, I'm not sure whether any of these are a good choice to experience the problem for myself: https://jupyter.org/try You could check Firefox's Web Console to see whether messages there point toward any obvious issues. You can open the Web Console in the lower part of the tab using either: * "3-bar" menu button > Web Developer > Web Console * (menu bar) Tools > Web Developer > Web Console * (Windows) Ctrl+Shift+k Then reload the page in the upper part of the tab and watch for error or security messages. (The lines with blue triangles generally are not significant unless you suspect a style rule problem.) Anything that sounds like it could be relevant? ---- As a quick way to determine whether settings or add-ons could be an issue, you could try: '''New Profile Test''' This takes about 3 minutes, plus the time to test your problem site(s). Inside Firefox, type or paste '''about:profiles''' in the address bar and press Enter/Return to load it. Click the "Create a New Profile" button, then click Next. Assign a name like May2019, ignore the option to relocate the profile folder, and click the Finish button. After creating the profile, scroll down to it and click the '''Launch profile in new browser''' button. Firefox should open a new window that looks like a brand new, uncustomized installation. (Your existing Firefox window(s) should not be affected.) Please ignore any tabs enticing you to connect to a Sync account or to activate extensions found on your system so we can get a clean test. ''Do your Notebook site(s) work any better in the new profile?'' When you are done with the experiment, you can close the extra window without affecting your regular Firefox profile.