Firefox drop downs do not reverse text color when link is selected

I have firefox 61.0.1 (64 bit). Something has happened with my drop down from all menu bar items. Example: click on bookmarks, get a drop down. All entries have light gray background, black text color. Click on any item in that drop down, background color changes from light gray to dark blue. In the past, when this happened, the color of the text on that item has changed to white automatically (so it can be seen), now it stays black (and it can't be seen). What could I have done to cause this change? What can I do to fix it? I've even reinstalled firefox to no avail. This problem does not occur on other drop downs (like windows explorer)