For errors that cannot be investigated with a screenshot of your site or the sitebuilder, it may be necessary to open the browser console.

Go to the page where the error appears and click F12 on your keyboard to open Developer Tools.
Click the Console tab if it is not already selected. This is the same for both Chrome and Firefox.
- If there appears to be a large amount of code under the Console tab accompanied by a scrollbar, you have the option of enlarging the dock to fullscreen. For Chrome, click the dotted line near the X to expand the "Dock side" option and click the icon for "separate window".
  
  For Firefox, click the "separate window" icon near the X.
Reload the page by clicking F5 or by clicking the reload button to the left of your browser's address bar.
Take a screenshot of the entire browser, including the address bar as well as the console. Send your screenshot(s) to a Support agent as an email attachment.

More information on browser consoles: