What? You are using more than 3.5GB of memory for your browser? I consider myself a heavy user with 20-30 tabs open at any one time. I used to have a 2GB memory usage with Adblock Plus and since switching to uBlock it averages 0.6GB of RAM.

64bit will open more address space but it has proven in the past to slow the browser down, the wider memory pointer size has a detrimental effect, Waterfox is Firefox recompiled as 64bit and other compiler optimisations: http://www.networkworld.com/article/2185649/applications/fas...

Not everything should be 64bit.