It's not possible without a DLL as far as I know to enumerate the programs that are running in your taskbar.
It is possible to get a list of running processes, but that would only show mozilla.exe etc. not the title of the Mozilla window.
The only thing I could do for you is enumerate the titles of your IE windows that you have open, as I know IE has a COM object interface. I don't know if Mozilla has activex support by default (I don't use Mozilla), though if I remember correctly there is an activex plugin for Mozilla. Look on google for that plugin, and check to see if there's any interface that can tell you what the window title is.
Also, I don't know if Mozilla supports $dde, because with IE you could use $dde in mIRC to retrieve the title of the open IE window.
Btw what do you eventually plan to do with the window titles? You might be trying to do something that doesn't require for you to have the window title in the first place...