On the free viewer the right click menu is still showing annotation options, if you click any of them it will infinitely log a lot of errors to the console.
This is happening even in your demo, e.g. go to PDF.js Viewer Demo | PDF.js Express open the console, right click in the viewer somewhere, click any of the annotation buttons.
This issue is still a problem in 8.7.2 and the demo viewer 8.7.2. No annotations enabled but right click and you can see the options. Clicking on any option throws a lot of console log errors.
We’ve added the issue to our backlog to be worked on in the future. We don’t have a timeline for when it will be fixed but if it does get fixed we’ll let you know when it’s available in an experimental build to test out and the estimated official release date.