My Firefox sync does not work for all history

Factual Questions
1

After sync my Firefox history drop down menu does not show the history for one computer.

History>Show All History>Today is the same on both computers.

The back arrow, click and pull down does work.

Only the drop down menu is missing history for only one computer.

How should I proceed to diagnose and fix this problem?

2

[Bump up once to see if the weekday morning crowd has any thoughts.]

I found a place that says to click on the ''Firefox button" and select preferences but I cannot find any Firefox button that leads me to selecting anything.