Example digits „1301“ could be following:

1. PIN (Computer, Phone, Game, TV, ATM, Locker, KeyLock ...)
2. Year (Chinese, ...)
3. Hours and Minutes
4. Day and Month
5. Phone number (Services, ...)
6. Number of letter (0 - [Space], A - 1, B – 2, C – 3, ...)
7. Lipstik (Leet Speak)
8. Number (Hex, Dec, Oct ...)
9. Part of registration plates
10. Reversed or scrambled
11. Combination any of these above
12. Random digits
13. Something else

FireFox Keyboard Shortcuts

Firefox:
CTRL + SHIFT + P (Private Browsing)
CTRL + T (New Tab)
CTRL + ALT (Switch between tabs)
CTRL + W (Close Tab)
CTRL + H (Show/Hide History)
CTRL + U (View Source) [19.10.2023]
CTRL + I (Page Info) [18.12.2023]
CTRL + J (Shows downloads)
CTRL + F or F3 - Find/Find next
F5 (Refresh webpage)
F11 - Full Screen Mode/Exit Full Screen Mode
ALT + Left Arrow - Page Back (12.09.2020)
ALT + Right Arrow - Page Forward (12.09.2020)
ALT, f, x (EXIT)