Text editing pop-ups in ABrowser not displaying or allowing editing of text

Abrowser 62.0 (32-bit)
Hardware: https://www.coactivate.org/projects/disintermedia/bishop

Text editing pop-ups are blank and stay blank, clicking on them does not create a cursor, and in some cases they don't accept entered text.

Steps to reproduce:
* go to about:config
* find any key with a string value (eg browser.sessionhistory.max_entries)
* right-click the value
* left-click 'Modify'
* click in text editing field of the resulting pop-up - no cursor
* type in text editing field of the resulting pop-up - no change in the value