Firefox functionality "Bookmark this page" does not work on newly imported bookmarks

Hi Forum,
(As I am new to both Qubes and this forum, please feel free to point me in the direction of a more appropriate category, or move it there).

I’m using R4.3-rc4 with debian-13, debian-13-xfce and whonix-18-… templates.
That cube uses a debian-13-xfce template.
Firefox version ist 140.6esr (64-bit).

After installing Qubes, I took the ‘personal’ Qube (green here) and imported my bookmarks (from HTML) in Firefox.
The bookmarks are now there between reboots.
But if I try to add some new one (Start-menu or CTRL+D), then the original or default start bookmarks layout appears. There is no trace of the imported bookmarks.
I expect to be able to add that bookmark to the current collection.

Thank you for your hints in advance

This doesn’t sound like it involves anything specific to Qubes OS, like disposables or inheritance from templates. Maybe try Mozilla’s Firefox Community Forum?