Hi Marjorie
I was the same problem and it was fault of my plugin ADBlock. https://addons.mozilla.org/fr/firefox/addon/adblock-plus/
Try without ADblock enable.
Thank you very much for your suggestion! Yes, this did it! I deactivated Adblock in Mozilla Firefox, this time also the "Advanced constraints" of 773 $t could be opened (while 773 $w and all other fields could be opened with Adblock activated). So this means Koha is ad-friendly? I hope not. However, of course I did reactivate Adblock. I also made note of this in the filed bug https://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=17660 Best wishes: Michael -- Geschäftsführer · Diplombibliothekar BBS, Informatiker eidg. Fachausweis Admin Kuhn GmbH · Pappelstrasse 20 · 4123 Allschwil · Schweiz T 0041 (0)61 261 55 61 · E mik@adminkuhn.ch · W www.adminkuhn.ch