One of my favorite secret features in TB3 is the fact that I can hit Cmd-1 and it will bring up the 3-pane window, even if it's been minimized in the dock. That feature isn't quite complete yet: 1) if the activity manager window is the only visible window, it won't work 2) I want the same for Cmd-N creates new message window 3) there are likely other shortcuts that we want to enable in these weird states that the mac gets in. cc'ing philor as I suspect he has a clue what's going on or not.
You don't want (or if you do want, we want you not to want) that for cmd+N, because cmd+N is "Create a new compose window" and cmd+N+N+N+N is "Create four new compose windows." A keyboard shortcut for "focus the most recently used compose window if there was one, or open one if there wasn't" might be nice, other than the way we're awfully close to "if you want a keyboard shortcut, choose the feature that's already using the key you want, remove that feature, and then we'll have a key free." The way that you get it to work is through a convoluted set of calls to pointless functions, toMessengerWindow() which just calls the actual function, toOpenWindowByType(). The <window> in messenger.xul has a windowtype="mail:3pane" attribute, which toOpenWindowByType uses (by way of Ci.nsIWindowMediator) to .focus the most recently used window with that windowtype, or if there isn't one, opens a new one. Oh, and it not working in the activity manager would be that same problem as whichever bug it was where you were asking about how to get menus showing when the activity manager is up, since although you could cheat and just include the <key> for your favorite shortcuts directly in the activity manager's XUL, the right thing to do is to have that shortcut work because it's the shortcut associated with a menuitem that's available from the activity manager, so we still need to suck it up and imitate Fx's browser-menubar.inc and friends.
Not just Mac?? In windows, ctrl+1 focuses 3-pane from AB and message compose. But not from Error Console, Message FIlters, Search Messages, and (as you point out) activity manager. we also have: bug 480268 cmd+0 as a shortcut for the Activity Manager window on OSX (why is this limited to Mac?) bug 395596 provide Ctrl+Shift+F to do "search messages" from compose window Bug 472785 Create about:hotkeys or about:keyconfig for Help menu Note: apparently Ctrl+2 invoked AB at one time but no longer works in windows