I work on an iMac and Firefox for some reason stutters every couple of minutes. It’s UI locks too often and breaks my concentration.
I now use Opera Developer Edition. It’s really fast and uses Webkit to render things. It has the familiar developer tools if you use Chrome (exact same tools) and you can even seamlessly install Chrome extensions in Opera.
It also comes with it’s own baked in AdBlocker that’s faster that uBlock Origin!