On any of Slashdot’s Post Comment pages—this, for example:
...
Logged-in users aren't forced to preview their comments. ...
Now forcing users—whether Anonymous Cowards or not—to preview sucks. I hate it. And it’s stupid considering I can get rid of it. Here’s the Greasemonkey script you’d require. It adds a ‘Submit’ button on the page, and sets a hidden variable op—which, apparently, Slashdot uses to identify whether it’s a preview, or submit, or whatever—set to value Submit.
Well, I thought that alone would have done the job. Turned out there’s some more weird shit that it does internally—and I’m not terribly sure what all. My guess is that it does some session stuff, where it sets some flag to indicate that the comment-to-be-posted has been previewed. So, the script, when you click on submit, first does a xmlhttpRequest with op=Preview, and then submits the form. Seems to work.