URL Keybinds (Command-Based) ავტორი ccc333

Mozilla-legal version of URL Keybinds (https://github.com/CCC000i/Firefox-URL-Keybinds).
Shortcuts can also be changed in about:addons -> Gear -> Manage Extension Shortcuts.

Limitations:
1. Native Firefox keybinds can't be overridden, and total number of shortcuts is hardcoded to 99. Lots of obscure stuff that's not even exposed by about:keyboard, like Alt+A and Alt+C, can't be bound.
2. Firefox-internal pages starting with "about:" can't be linked to.