Thanks lanux128, I'll think about that.
Here are the raw settings if anyone is interested (requires keyconfig):
user_pref("keyconfig.main.xxx_key__DownThemAll! (All tabs)", "alt control][A][][DTA_ContextOverlay.findLinks(false,true)][");
user_pref("keyconfig.main.xxx_key__DownThemAll! Manager", "alt control][J][][DTA_AddingFunctions.openManager()][");
user_pref("keyconfig.main.xxx_key__DownThemAll!", "alt control][D][][DTA_ContextOverlay.findLinks(false,false)][");
user_pref("keyconfig.main.xxx_key__dTa OneClick! (All tabs)", "alt control shift][A][][DTA_ContextOverlay.findLinks(true,true)][");
user_pref("keyconfig.main.xxx_key__dTa OneClick!", "alt control shift][D][][DTA_ContextOverlay.findLinks(true,false)][");
I used the functions for keyconfig (another add-on) to create them, which provides a nice GUI.
Also any feedback on whether these shortcuts seem fairly sensible and conflict-free for most Firefox users is welcome.
DownThemAll! (All tabs) = Ctrl-Alt-A
DownThemAll! Manager = Ctrl-Alt-J
DownThemAll! = Ctrl-Alt-D
dTa OneClick! (All tabs) = Ctrl-Alt-Shift-A
dTa OneClick! = Ctrl-Alt-Shift-D
The logic behind Ctrl-Alt-J is that it is similar to the builtin Ctrl-J (Tools > Downloads)
And the All Tabs shortcuts are intended to be reminiscent of Ctrl-A (select all) although I don't know if that exists on all platforms.