For hardware, Facebook gives me a very nice laptop: 15-inch MacBook Pro Retina with 2.8 GHz i7, 16 GB RAM, and 1 TB SSD – and a 27" display at my desk.
I don't use much fancy software – mostly Chrome and MacVim. I often avoid fancy debuggers and just resort to "printf debugging" and add console.log statements. Some of my development work is on a remote server in the Facebook datacenter, and I recently set up iTerm 2 with tmux integration so that it's easy to create new tabs and to restore my windows after switching networks. It's so much better than just using SSH alone.