I posted from my laptop and used Aurora (Firefox) running on Ubuntu so... technically, yes but in a rather unsatisfying way.
Why is that unsatisfying? And why is it just "technically" open source, is it not open source in spirit as well?
Oh, yeah. Ubuntu and Firefox are completely and satisfyingly opensource but the answer isn't because I didn't use the very phone I was praising. Technically, I used an opensource app but not in a way that would support my point.