Comment 2 for bug 1675501

webbrowser-app uses a standard TextField component with no specific handling of the context menu, so that would be a bug in the UITK.
I am not seeing that issue, however I am seeing one that might be related: in my testing, the paste option in the context menu is always greyed out, regardless of the contents of the clipboard. Pasting with the Ctrl+V keyboard shortcut works, but cannot be done from the context menu.