That is not possible. You can't disable or change these accelerator keys. You will have to use another shortcut like Alt+Ctrl+E. Note that Alt+Shift is reserved for access keys on web pages including about pages like about:preferences.

Firefox doesn't currently have a way to let extensions take over built-in keyboard shortcuts. I hope that is added in the future.

Interestingly, Alt+e doesn't give the warning that it is a built-in keyboard shortcut, even though it is a menu hotkey. I wonder why not??

For Windows

You could completely disable Alt from triggering menus on the menu bar as a workaround. Then instead of Firefox intercepting Alt+e for that purpose, the keyboard shortcut will pass through to other processes. Here's how:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

(2) In the search box above the list, type or paste menuacc and pause while the list is filtered

(3) Double-click the ui.key.menuAccessKey preference to display a dialog where you can edit the value from 18 to 0 (that's a zero) and then click OK.

(4) Do a normal Firefox Exit and restart.

Note that it isn't advised to make changes to these ui.key.* prefs. You can easily forget about this change and then wonder why you can't use the Alt key to access the Menu bar (i.e. you need to use F10 or have the menu bar visible permanently).

jscher2000 said

. . . For Windows You could completely disable Alt from triggering menus on the menu bar as a workaround. Then instead of Firefox intercepting Alt+e for that purpose, the keyboard shortcut will pass through to other processes. Here's how: (1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk. (2) In the search box above the list, type or paste menuacc and pause while the list is filtered (3) Double-click the ui.key.menuAccessKey preference to display a dialog where you can edit the value from 18 to 0 (that's a zero) and then click OK. (4) Do a normal Firefox Exit and restart.

This is a very interesting idea. I tried it, and it did in fact disable the ALT trigger, but the ALTs did not pass through. There may be something else blocking them.

By the way, the add-on I'm using is FoxScroller. I want to define ALT-<anykey> as the START/STOP shortcut.

jscher2000 said

Firefox doesn't currently have a way to let extensions take over built-in keyboard shortcuts. I hope that is added in the future. Interestingly, Alt+e doesn't give the warning that it is a built-in keyboard shortcut, even though it is a menu hotkey. I wonder why not?? For Windows You could completely disable Alt from triggering menus on the menu bar as a workaround. Then instead of Firefox intercepting Alt+e for that purpose, the keyboard shortcut will pass through to other processes. Here's how: (1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk. (2) In the search box above the list, type or paste menuacc and pause while the list is filtered (3) Double-click the ui.key.menuAccessKey preference to display a dialog where you can edit the value from 18 to 0 (that's a zero) and then click OK. (4) Do a normal Firefox Exit and restart.

Thanks a bunch. This helped me free Alt+s. I am on Linux Mint and this is a browser based feature and not Windows specific, I suppose.