Nearly 400 tabs open across several browser windows. Firefox with Tabmix plus and noscript addons. Performance and memory use is very comfortable with very few browser crashes.
I use Chrome for websites that use huge amounts of JavaScript links, which are pain to use with noscript. Chrome does not like a lot of tabs open and chews up memory and performance if forced to run large numbers of tabs.
Firefox is going for at most N+1 cores worth of processes, as I understand it (one per core for websites and one extra for compositing and the UI) and is doing to use cooperative threading (Quantum DOM) to improve responsiveness within those processes without the overhead of running a process per website.
I use Chrome for websites that use huge amounts of JavaScript links, which are pain to use with noscript. Chrome does not like a lot of tabs open and chews up memory and performance if forced to run large numbers of tabs.