However, browsing the Chimera prefs.js file I noticed a particular user_pref line:
user_pref("browser.always_reuse_window", true);I added that line to my Mozilla:user.js file (in the same directory as the prefs.js file, ~/Library -> Mozilla -> Profiles -> Username -> [random].slt), restarted Mozilla and woila! External requests now load in the active tab. Mozilla doesn't create a new tab but hey, at least it doesn't create a new window!
Now if I could only figure out what the setting for opening a new tab with an external request is instead, I'd be in hog heaven!

