ui.submenuDelay settings not working

[onebigdawg]

Several years back, I changed the ui.submenuDelay setting to 500 from 0. It worked quite well.
For some reason, the setting reverted back to 0 this week. So I set it back to 500. The delay worked just like before as long as I didn't close FF. Unfortunately, as soon as I closed FF, ui.submenuDelay reverts once again back to 0.
How can I make this change permanent?
Windows 7 Ultimate, FF 57.0.4 (64-bit)

[dickvl]

Do you lose other setting changes you made when you close Firefox?
http://kb.mozillazine.org/preferences_not_saved

https://dxr.mozilla.org/mozilla-release ... ndFeel.cpp

[onebigdawg]

Thanks for the help, however, I can change other settings and they are saved just fine.
the ui.submenuDelay settings keeps reverting back to 0 when I close FF and then reopen it, even though I change it to 500.
Has FF somehow decided that they don't want us having a delay in the menu popups?