In Firefox 3.6 on Windows you can hide the menu bar via "View > Toolbars" or via the right click context menu on a toolbar. Press and hold the Alt key down to bring up the menu bar. Go to "View > Toolbars" or right-click the menu bar or press Alt+V T to select which toolbars to show or hide.

See also Restore the Menu bar in Firefox

Thanks co-rel. It worked fine. Is there any way to make the menu bar permanently visible? I'd also like to know how to remove some of the toolbars that I don't want anymore.

You can go to View > Toolbars and put a check-mark before the toolbars that you want to see and remove the mark if you want to hide a toolbar. You can do the same by right-clicking the menu or navigation toolbar.

So there's no way to have File Edit View Tools etc. visible all the time? I have to press Alt every time I want to see them?

Make sure that the "Menu Bar" is check-marked: View > Toolbars

I see Toolbars under View but can't figure out how to place a check mark next to it.

You can click on a toolbar entry in that list (View > Toolbars) to toggle the display status between hidden and display.