I use Firefox too, as I don't really trust chrome with privacy, and Chromium is basically just built off it. I think it's probably safe to use though. I still keep it handy as if a site refuses to work in FF because of adblock etc and I really need to get to it, I just use Chromium, which I have zero extensions installed in.
I've never had any issues launching it though so can't help with that. I presume you used the package manager? You should be able to uninstall and reinstall. I find LM18 has some weird quirks at times with certain programs though. The other day I was having issues with the calculator and a few other programs. The GUI would just not accept any kind of input. Ended up having to reboot the whole system.