Circle to Search is an OS feature, not a browser one. It is also a feature that's only been released on a handful of premium phones, so make sure it's available for your model. If it is, the feature should be available as a Setting in the 'Display' section (or just search 'Circle to Search' in your phone's settings).
I did find information on Samsung's site & although my phone does have the UI 6.1 update, my phone is not listed to have the Circle to Search feature.
Oh well, it does sound fast & easy in theory.
Update:
My phone completed a system update earlier today & I now have the Circle to Search functionality.
Now just have to get used to using it, the commercials make it look so easy. But it is working for me, cool!