Hi luckman212, what would you like Command+s to do?

Firefox doesn't have a built-in feature to re-map browser keyboard shortcuts. Web pages can intercept and repurpose many key combinations, and extensions like Saka Key take advantage of that to let you remap them to various other functions. I don't know whether it works for this one is particular.

https://addons.mozilla.org/firefox/addon/saka-key/

I would like to use ⌘S as a trigger key for one of my extensions (Bitwarden).

You can modify extension's keys via the about:addons page. Click the cogwheel button and look for Manage Extension Shortcuts.

That's not what I'm asking. I know you can set the keys- if you read the top post you'll see the question is about changing default keybindings, since ⌘S is already in use by FF's default "Save Page As..." command. And this is the key I want to use for my extension...

As far as I know, extensions cannot re-purpose built-in keyboard shortcuts using the commands property in manifest.json or the commands API. It may be under consideration for a future version, but for now, the only known workaround is a content script.

I found a solution, but it's not easy for most users.

I patched browser.dtd and broswer.xul and edited the keymappings directly, in accordance with the info I found here: https://github.com/nilcons/firefox-hacks#binary-hacking-automated

Using this method, I was able to remove the ⌘S shortcut and assign it to Bitwarden. I also removed a few other keyboard shortcuts that I didn't like: ⌘B, ⌘U, ⌘I, and ⌘D