Can not insert text before Mention

[susnux]

Describe the bug
The cursor can not move before a mention in Firefox, so if the first thing inside a document is a user mention, then you can not add anything before it.

This is a known bug in Firefox when a contenteditable=false element is the first child of a contenteditable=true. See upstream bug report https://bugzilla.mozilla.org/show_bug.cgi?id=1796943.

To Reproduce
Steps to reproduce the behavior:

1. Open empty file
2. Add a mention
3. Try to add something in front of the mention

Expected behavior
Cursor can move before the mention.

Client details:

• OS: Linux
• Browser: Firefox
• Version: master
• Device: desktop

[mejo-]

There's actually other objects with the same issues. Out of my head I think that tables at the beginning of the document have the same problem.

[mejo-]

Seems like the problem only exists in Firefox. In Chromium, I can move the cursor in front of a user mention even if it's the first node inside the document. Also reproducible in the Tiptap example at https://tiptap.dev/api/nodes/mention

Likely it's because of the contenteditable: false attribute for the user bubble. When removing the attribute, I'm able to navigate in front of the user bubble. But certainly that's not what we want 😉

I opened ueberdosis/tiptap#3320 upstream.