Some .ui files from Web accepted by GtkBuilder cannot be edited in Glade
Some of the .ui
files used by Web for dialogs cannot be opened in Glade (see epiphany#84 (closed) for the whole list), which exits with the following error:
GladeUI-ERROR **: Unable to get GladeWidget for internal child headerbar
The smallest of them is synced-tabs-dialog.ui, so probably it's a good one to start investigating this issue.
Edit: This happens with Glade 3.22 installed from Flathub (which is what I am using to discard any possibiliyu of my system being to blame).
Edited by Adrián Pérez de Castro