Useful Firefox HotKeys
Hotkeys or "Keyboard shortcuts" are programmed key or key combinations that trigger some function to occur. Hotkeys are Typically faster than using the mouse in any application. Here are a few Firefox Hotkeys I use on a regular basis.
Alt+right or left arrow - back & forward page navigation
Backspace - back to the previous page
CTRL+T - new tab
CTRL+L - Focus cursor on address bar
CTRL+TAB - Switch to next open tab
CTRL+SHIFT+TAB - Switch to the previous tab
CTRL+F - Focus the cursor on the find search box
TAB - Move the focus through elements in the page like links and form fields - Sometimes there are defined tab indexes which control the order of elements when tabbing. If there are no tab indexes defined TAB will move the focus to the next element in a 'top down' fashion. Try holding down tab to quickly move the focus through all elements on the page.
/ - Opens quick find as you type search
F3 - Find next occurrence of search term from above commands
F5 - Reload page
Home and End - Quickly jump to the top or bottom of the page
Page Up / Page Down - Scroll up and down the page or currently focused element.
CTRL+SHIFT+ + (plus) or -(minus) - Increases or decreases page zoom / text size
# Plugin specific hotkeys:
F12 - When using Firebug opens the firebug utility
CTRL+SHIFT+F - Open web developer toolbar element information viewer
In addition ALT + F, E, V, B or T and arrow keys are great for menu navigation.
I'm sure there are many more useful hotkeys out there. For reference here is Mozilla's official Firefox hotkey list.
I've also seen a few web sites that implement their own hotkeys which I think is pretty neat as long as there are no conflicts with OS or browser specific hotkeys. Here is one example, use J and K to navigate through the posts at: http://ffffound.com/.