Console doesn't log js errors from content script

The errors in the content script are not reported in the tab's Web Console due to Firefox bug 1410932, which is not fixed (as of Firefox 79, released on 2020-07-28).

I listed possible workarounds in another answer:

• use try..catch with logging,
• check the Browser Console (which does show errors from the content script)
• use the Debugger's "pause on exceptions" option.