What internet browser do you use?

Firefox portable with a few select security plugins is my favourite, and the most secure browser I've found so far.
As long as you don't allow it to do auto updates and block all the background connections to Mozilla services with a hosts file.

Firefox ESR 52 with uMatrix can still block the behind the scene / background channel, which Mozilla decided to hide in Firefox Quantum and the new web extensions.
Now Mozilla are able to sneak in their own google analytics past all the ad blocking extensions. Probably similar for chrome too.