Here are some handy  Firefox shortcuts that I use all the time:

1) crtl-k — puts the cursor in the google search box.

2) crtl-l (that’s an L) — puts the cursor in the URL box.

3) ctrl-tab –  switch tabs (forward)

4) ctrl-shift-tab  — switch tabs (backwards)

5) ctrl-t  — opens a new tab

6) ctrl-w — closes the current tab.

7) ctrl-shift-t  — reopen previously closed tab in the current window.  Press it again and open the previously closed tab, etc.