[millerm]

Well, for savvy users:

In the location bar type about:config

Search for javascript.enabled

You can turn it off there by simply double-clicking the entry.

[mannix]

Yeah, after you click a huge "VOID MY WARRANTY" button. I am surprised they made this change after the recent tor exit node exploit...

[sp332]

The "void my warranty " button is completely valid, since disabling JS will break many popular websites.