How to switch to ESS mode manually?

Question

I sometimes use emacs with the "It's all text" firefox extension to write in textareas, and sometimes I need to insert R code into the file, which is usually named something like "stackoverflow.com.231x234.txt", which is of course triggers the text mode. How can I switch to ESS mode manually in this case? I know I can do "M-x python-mode" for python, but I don't what the equivalent is for ESS.

Answer 1

M-x R-mode should do the trick.