I haven't been following exact features between browsers too closely recently, but Firefox's Tracking Protection has been around for a while and improving for years; and of course, Firefox is where AdBlock/uBlock originated. What does Safari provide that Firefox does not? How does it affect web compat?
> and Chrome made JIT exploitation and then Spectre attacks in JavaScript impossible by using process boundary separations and applying sandboxes to purpose built processes.
This feature has been a long time coming in Firefox, and it's still not all the way there.
But Firefox did just release an opt-in process isolation feature for Firefox, which applies stricter cross-origin controls for a variety of content, and in exchange gives web developers access to SharedArrayBuffer, the feature that needed to be disabled to mitigate Spectre attacks.
So site isolation is progressing, and the first iteration of it has been released.
> What awesome technical choices do you think Mozilla has made recently?
The development of Rust. Servo, which acted as an experimental testbed for a parallel browser engine and has led to its CSS parser, WebRender, and a number of other components being used by Firefox. Asm.js as an alternative to NaCl, which led to the joint development of WASM.