[Firefox] Cannot type before a mention.

[shved270189]

Steps to reproduce:

1. Open a page with the Lexxy editor in Firefox.
2. Add a mention.
3. Place the cursor before the mention.
4. Start typing.

Actual result:

Nothing happens.

Expected result:

The text should be typed.

Screen.Recording.2026-06-22.at.11.57.34.mov

[lyubomir-bozhinov]

I'd like to pick this one up, if nobody else is on it.

Initial trace, for what it's worth: mentions are inserted as CustomActionTextAttachmentNode, which extends Lexical's DecoratorNode (src/nodes/custom_action_text_attachment_node.js), so they render as contenteditable="false" islands inside the editable root. That points at caret placement at a decorator boundary in Gecko rather than anything mention-specific — #1148 may well share the same root.

I'll confirm against a real Firefox before proposing anything.