webrepl serves on a unencrypted websocket, which means that it can't be accessed from a page served over https.

The simple workaround is to manually ensure that you use http://micropython.org/webrepl/ instead of https://micropython.org/webrepl/

Some ideas to improve this:

• Make webrepl.py on the device support wss
• Load the page from the device instead -- i.e. serve a bare-bones webrepl.html that includes all its resources and content from a remote site (this could be done in ~100 bytes or so... not much more than just a script tag).
• Make https://micropython.org/webrepl/ redirect to http://micropython.org/webrepl/ (This is a bit backwards...given that we should be doing the exact opposite via things like HSTS these days).