Content script not loading in Salesforce CKEditor 4

[twschiller]

Describe the bug

Selection popover not displayed in Salesforce CKEditor

To Reproduce

Steps to reproduce the behavior:

1. Define a context menu
2. Try to select some text in the email editor: https://pixiebrix3-dev-ed.lightning.force.com/lightning/r/Case/5008X00002YDcUtQAL/view

Actual behavior

The tooltip container exists in the DOM, but is not visible. So the contentScript appears to be partially loaded

Expected behavior

User can see/click on the a selection menu item

Screenshots/Loom

Desktop (please complete the following information):

• Browser: Chrome
• Extension Version: 1.8.11 (MV2 and MV3)

Discussion/Investigation

• Salesforce appears to be on CKEditor 4
• Salesforce has to layers of iframes for CKEditor, one for the editor and one for the editable area
• I don't think the content script is fully loaded within the editable area
• It might be because the 2 URLs (of the editor and editable area the same)?

If you try the context menu, you get the following error:

Additional context

Add any other context about the problem here.

• What mod(s) were you running?: writing assist
• What website(s) were you using?
  • https://pixiebrix3-dev-ed.lightning.force.com/lightning/r/Case/5008X00002YDcUtQAL/view
• Do you need any special permissions to reproduce?
  • See [email protected] credential in 1Password