Press the Alt or F10 key bring up the tool bar,

I ended up restarting my computer and it's there now. Thank goodness! It just got be too frustrating to continue working without it.

UPDATE: FORGET WHAT I SAID ABOVE! Oct 8, 2016 This continues to be a problem- ongoing since posting here in July. At first the menu bar would reappear after a restart but them stop appearing all together. I recently did a firefox "reset"- it was after being asked if I wanted to do that shortly after and update. Eventhough it warned Id loose all my customizations, i gave it try. It worked! But only for about a 1.5 weeks.

Well done.

Okay- I woke up and it's gone again! f10 is the volume and alt f10 brings up sound preferences.

Sounds like you have a laptop with a specialized keyboard.

Alt alone should work to temporarily reveal the Menu Bar.

But you can have the Menu Bar showing all the time, like this: Right-click ate the top of the browser window and select Menu Bar so that it has a check-mark.

The Mac works a bit differently than other platforms: the operating system takes control of the top bar and Firefox's internal enable/disable for the menu bar is not applicable.

This old thread from last September lists a number of things you could check, including Firefox's xulstore.json file which sometimes becomes corrupted, and Mac's plist file, which I know nothing about:

How can I get back the missing menu bar when using Firefox (latest version) on a Mac (that uses the latest version of OSX)?

I'm sorry but that is all too confusing for me with no menubar options. This just very recently became an issue on my machine- I am using a macbook pro with an external apple wireless keyboard & an external Samsung monitor S22C300. Problem remains unsolved.