Do you only want to disable "Ctrl+T" (open new tab) or also "Ctrl+Shift+T" (undo closed tab) ?

You can disable "Ctrl+T" via the autoconfig.cfg file. For "Ctrl+T" you need to disable key_newNavigatorTab For "Ctrl+Shift+T" you need key_restoreLastClosedTabOrWindowOrSession

• https://support.mozilla.org/en-US/kb/customizing-firefox-using-autoconfig

See this answer for a possible way to disable specific keyboard shortcuts:

• /questions/1378404#answer-1510431 Disabling Control +w keybind

You need to replace this line:

let keys = ["key_close","key_closeWindow"];

With this line:

let keys = ["key_newNavigatorTab","key_restoreLastClosedTabOrWindowOrSession"];

Yes, thank you! Ctrl+T was the primary one I was having trouble disabling. The Shortkeys add-on handled pretty much everything else.

Part of the challenge is figuring out what Mozilla calls the function you are trying to disable. In the Ctrl+T example, it was called "newNavigatorTab"... if you don't know that, you're kind of stuck.

Of course, now it appears Ctrl-N is not being blocked... trying to find the name for THAT function, now that I've let the config.sj genie out of the bottle! LOL That also opens a new tab, but in a new window.

Ctrl+N: key_newNavigator Ctrl+Shift+N: key_undoCloseWindow

• https://searchfox.org/mozilla-release/source/browser/base/content/browser-sets.inc
• https://searchfox.org/mozilla-release/source/browser/base/content/browser.js

Is there a complete list somewhere of what shortcut keys call which function? The few that have been passed on here are great, but it would be helpful to have a comprehensive list.

You can look at the Browser Toolbox.

• https://firefox-source-docs.mozilla.org/devtools-user/browser_toolbox/

To enable the Browser Toolbox, use this in the Web Developer Tools Settings (press F1 on any of the devtools like the Inspector).

• select "Enable remote debugging" in the Web Developer Tools settings
• https://firefox-source-docs.mozilla.org/devtools-user/settings/

Sadly, I cannot see anything related to the actual keystrokes that invoke the functions. I suspect there must be a comprehensive list out there somewhere (I can't be the first person to want this LOL).

Within a key tag, you can find the key in the key attribute. The modifiers attribute set what modifier key(s) like Shift (shift) and Ctrl (accel) and Alt (alt) you need to press. The data-l10n-id attribute gives some clues about the action and the command sets the action.

Ctrl+N -> key_newNavigator -> window-new-shortcut -> cmd_newNavigator

 <key id="key_newNavigator" data-l10n-id="window-new-shortcut" command="cmd_newNavigator" modifiers="accel" key="N"/>

Ctrl+Shift+W -> key_closeWindow -> close-shortcut -> cmd_closeWindow

 <key id="key_closeWindow" data-l10n-id="close-shortcut" command="cmd_closeWindow" modifiers="accel,shift" key="W"/>

Alt+CursorBack -> Browser:Back

 <key id="goBackKb" keycode="VK_LEFT" command="Browser:Back" modifiers="alt"/>

You would have to search the source code to get more information about a specific key code and action, there are usually explanatory comments.

• https://searchfox.org/mozilla-release/search?q=key_newNavigator&path=

OK... maybe I'm blind to something here... I can find code with the <key id=...> in it, and it includes everything, such as the data-l10n-id, the command and the modifiers... but no actual key= part. Where are you finding that?