***Important: You have to refresh already opened web pages after installing shortkeys to make it work on them, better yet - restart the browser after installing the extension. If your shortcut does not work when an input is focused, this can be turned off in Shortcut Options -> Activation Settings -> ticking the option Active while in form fields Current limitations based on the Firefox API (more details on github):

shortkeys only works in the context of a loaded page. What does *NOT* work is: new tab page, addons page, or any other internal pages such as about:config,about:newtab,about:addons, etc.
shortkeys cannot override Firefox default shortcuts such as: ctrl+j, alt+d and others using the "Do nothing" action *outside of the webpage* e.g. the default firefox chortcut will still work in the url bar/ search bar
shortkeys does not work in the url bar or the search bar, it only works in the context of a webpage
shortkeys will start working when the page has finished loading, not *right* after you opened a page, or clicked a link (this annoys me, too, but yeah - API Limitation:(

Shortkeys makes it easy to add custom shortcuts to your browser for the following actions:

Run custom JS
Do nothing (for disabling a Firefox shortcut you don't like, in the context of the page, not the whole browser window - explained above)
Open a bookmark or bookmarklet
Scroll up/down/left/right by a little or a lot
Scroll to the top or bottom of the page
Go back or forward in history
Jump to existing tab by URL
Open new tab with URL
Switch to the previous/next/first/last tab
Create a new tab or close the current tab
Clone the current tab
Close all (unpinned) tabs except for current tab
Reload the page
Copy the current URL
Pin/Unpin the current tab
Move the current tab left or right
Zoom in/out/reset
Blacklist or whitelist specific shortcuts on specific sites
Clear downloads (page and bar)
Click button and switch to next tab (for Tribal Wars players)

Shortkeys allows for enabling or disabling key combos while you're currently focused on a form field, so you can have keyboard shortcuts like "r" or "shift+h" and still be able to type those values into a form without triggering the shortcut if you want. You can also blacklist or whitelist sites per-shortcut, to pick and choose which shortcuts you don't want active on which sites (this field also supports regular expressions in the following format: /regexp/). Shortkeys lets you use pretty much any key combo you want. Key combos are zero or more modifier keys (including ⇑, shift, option, ⌥, alt, ctrl, control, command, and ⌘), and one action key (letter, number, punctuation, or special key shown below), combined with + signs. Examples: "shift+r", "k", "ctrl+alt+f7", "command+pageup", etc. You can also string multiple key combos together to make key sequences (like how Gmail has "g i" to go to inbox). Examples: "g g" or "ctrl+t shift+f7". Special action keys that can be used include backspace, tab, clear, enter, return, esc, escape, space, up, down, left, right, home, end, pageup, pagedown, del, delete and f1 through f19 (make sure the F keys are specified in lowecase e.g. f1).

Permissions Required Shortkeys requires the "Your data on all websites" permission because it's the only way to inject JavaScript code into every page, and injecting JavaScript code into every page is the only way to get Firefox to recognize custom shortcuts. If you try to register key listeners (i.e., create shortcuts) outside the context of the page, then they will be ignored by Firefox. I promise that the code that runs on the pages you visit only checks the URL against the blacklists you have set, and adds the shortcuts if they're not blacklisted. That's it. Shortkeys also requires read/write clipboard permissions so that import and export from clipboard can function. If you're still nervous, you're more than welcome to look at the source code: https://github.com/mikecrittenden/shortkeys

Developer response