Try this -Strange because I'm also on Debian 12 with KDE but I had problems.
Drag & Drop bookmarks in Firefox does not work for instance.
1) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.
(2) In the search box above the list, type or paste urlb and pause while the list is filtered
(3) Double-click the browser.urlbar.trimURLs preference to switch it from true to false.
now close and reopen Firefox - this worked for me