Sorry, your screen shot did not come through. You can try attaching it to a reply to yourself, https://support.mozilla.org/questions/1069129

Do you notice any pattern of what URLs appear in the dialogs? For example, internal URLs starting with chrome:// or resource://, or scripts in the site itself? If you see a lot of internal URLs, look for anything in the path that might indicate a particular extension is involved. Something might have changed in Firefox that created a compatibility issue.

I uploaded the screenshot. Occasionally I get another identical script warning, with the address ending in 61 or 49.

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

It's frustrating that the entire address isn't shown. When I search that last part:

data/jquery-highlight1.js

I find threads about script errors with an extension named Greenhouse. Try updating or disabling it on the Add-on page. Either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Extensions. Then:

• To update, click the "gear" button above the list and "Check for Updates"
• If no updates are available, find that extension and click its Disable button

Often a link will appear above a disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step.

Any improvement?