The Empty Cache Button add-on normally works well but it is not currently working with v32 Aurora or v33 Nightly Firefox builds. It still works well with both v31 Beta and v30 Release Firefox versions.
I use this constantly. Be it a web dev or netadmin, Firefox aggressively caches and can make you crazy as you develop content or have a lot of DNS changes. This makes it so easy to just get things working again.