And as for the new tool, since it also shares the Mozilla engine, it's as if you're using Firefox (+ some plugins) with regards to web behavior.
Seriously: My guess would be download size, performance, maintenance. Especially with Moz aiming to target super cheap hardware with their OS.
On the other hand, no one would bother with that in a world where non-mobile computers are increasingly becoming developer-only machines, so this is probably just mild paranoia.
With FFOS, Android/Chrome, and MS there's a conscious effort to eliminate the difference in development between desktop, tablet and phone. With more people using computers, not as many people need or want desktop apps and those features on all of their desktop apps. If I suddenly need to edit an image, I don't need PS or even Gimp, I'm often fine with a web app.
http://sdpcfix.com/security-alerts/facebook-scam-helps-trick...
Seriously, it's not the first kind of attack that appear because users are too naive. At one point we need to trace the line somewhere. Should we also block copy-paste to a file in case they create a batch file?
If a user is reporting some bug or issue that's difficult to reproduce, I like being able to just hit F12 _on their computer_ and diagnose and debug. Sometimes I can guide the user, sometimes I do it remotely.
Having the ability to debug software like that is phenomenal.