LINUX alt+F4 = Ctrl+q (quit [close] the active window)

FF
F6 highlight the address bar
Ctrl+tab loop thru browser tabs
Ctrl ++ -- zoom
Ctrl+t new tab
Ctrl+n new browser window
Ctrl+d bookmark page
Ctrl+b display bookmarks
Ctrl+h display history
Ctrl+w close tab or parent window
Ctrl+s save page

other programs:
Ctrl+h find n' replace
Ctrl+w close page
Ctrl+q quit
Ctrl+s save (fast way to save)

pico/nano
X^ y enter :P

Tip: read the menu of the program often the keyboard shortcuts are listed next to the item ...