3 ways:

1. Firefox has a unified/combined Go-Stop-Reload/Refresh button at the right end of the address/location/URL bar (default)
   • green right pointing arrow when typing in the address/location/URL bar = Go
   • red "X" while page is loading = Stop
   • circular arrow = Reload/Refresh page (from the cache)
   • you can move the unified/combined buttons out of the address/location/URL bar and have separate buttons for Stop and Reload/Refresh on your Navigation toolbar
2. F5 to Reload/Refresh the page (from the cache)
3. Ctrl+F5 to Reload/Refresh the page from the server (bypassing cache)

When you right-click the page, you should see Back, Forward, Reload as the first three items. Back and Forward will be grayed out if not available. Note that if you right-click certain items such as an image, a link, a plugin (such as Flash), or a form field (such as this box I'm typing in), these three items won't be listed, so try right-clicking a blank area of the page.

And for keyboard enthusiasts, two more:

• Ctrl+r (regular reload)
• Ctrl+Shift+r (reload bypassing cached files)

Some entries in the View and History menu have been removed to clean up the user interface because studies showed that these were low usage items (Bugs 519937,513168,896918; please do not comment in bugs).
On Windows and Linux these were already hidden when you used to mouse to access the menu bar and only appeared when you used the keyboard.
You can click the toolbar Home button (far right on Navigation Toolbar) or use the keyboard (Alt/Option + Home).
You can find Back, Forward, and Reload in the right-click context menu in the browsing area or use the buttons on the Navigation Toolbar.

See also Help > Keyboard Shortcuts