Ahhh, I figured it out, when I ran the wrong version of geany (see #3451) specifying this config it probably wrote the LM system defaults. Nothing a quick delete won't fix :-). So yes its Ubuntu that sets those values for terminal and browser, but thats totally allowable for distros to do that, they may not provide xterm or firefox by default.
@ntrel I totally agree that results should be checked, but I'm not sure what Geany can do if it detects failure (except write some message to debug).
Possibly one of the solutions from #2444 or #3178 might be better than fixed values, security oriented distros, lightweight distros, libre oriented distros, all commonly change the browser (even if its a de-trademarked firefox, its name changes). I wouldn't worry if the solution is Linux specific, windows and mac are `#ifdef`ed anyway.
And users (me for eg) often prefer different browsers.