Here is the fix for the 401 problem with Canvas and Zoom using FIrefox:

Browsers increase security settings to provide users with more control over their privacy settings while navigating the web. These security settings also prevent tools nested within another tool (e.g., Zoom in Canvas) from validating user data required for the nested tool to function correctly.
 For Firefox, Zoom should be added as an exception to the third-party browser cookie blocking security settings to resolve this issue.

Firefox: Exempt Canvas and integrated tools from Enhanced Tracking Protection

  1. Log in to Canvas
  2. Click the Shield icon located to the left of the URL address bar
  3. Locate the "Enhanced Tracking Protection is ON for this site" message
  4. Toggle the switch OFF for Enhanced Tracking Protection
  5. Reload the page if needed