Ui.allow platform file picker
From MozillaZine Knowledge Base
Many users prefer the internal XUL file picker to the GTK file picker. In some cases, the XUL picker performs better than the native GTK equivalent. This preference allows you to choose between the native file picker for your OS or desktop, or the internal XUL version.
Possible values and their effects
Use the system file picker if available. (Default)
Use the XUL file picker even if a system file picker is available.
First checked in
Has an effect in
Linux versions of: