Current stable - 1.3.551.38 (32-bit) - wow!
Have just today switched to Vivaldi (on Linux Mint 17.2 - Cinnamon), after having previously used it a few times. I find it quite easy, intuitive (after a modest learning curve), fast, and with some VERY nice features. I'm a devoted Firefox user of many years, but memory issues with FF are making me slowly crazy. I see NONE of the problems I've been having with FF inV. No CPU racing, just no problems, period. Very impressive. At one time I was an Opera user, but left due to not being able to ditch the coupled mail client, which slowed launch, etc. Don't see that problem with Vivaldi. It just works, and stays out of my way. Well done. Ya got me!