Not sure where the best place for this is, but I thought people might find this useful:

Note: I've only verified that this works in Chrome and FireFox

If you'd like to have a live preview of the $math$ formatting as you type, you can use the following scriptlet:

---

javascript:if($("#wmd-preview:visible").length){$("#wmd-preview").hide().after("<div style='background-color: #dadada; border: 2px dotted white; font-size: 107%; clear: both; line-height: 130%; margin-top: 14px; padding: 3px; width: 660px;' id='math-preview'></div>"); $("#wmd-input").keyup(function() { jsMath.ConvertTeX('wmd-preview');jsMath.ProcessBeforeShowing('wmd-preview'); $("#math-preview").html($("#wmd-preview").html())}).keyup();$("input[value=Preview Math]").hide();}void(0);

---

To see what this does:

1. Go to a question or answer page on mathoverflow
2. Put the long string from above (from "javascript:" to "void(0);") into the address bar, hit enter.
3. Type something like $e^{\pi i}=-1$ in the editor, note that you see the preview update as you type (i.e. as soon as you type the second $, the preview will show the math)

To setup a scriptlet for easy use:

1. Create a new bookmark named "Live Math Preview" (or whatever)
2. Set the address to the long string above (from "javascript:" to "void(0)").
3. Put the bookmark in your links bar, so you can easily click on it
4. Whenever you're on question or answer mathoverflow page, just click that bookmark link. You'll notice that the "preview math" button disappears, and the preview will show the math formatting as you type it.

Thanks danlec! It should work for everybody automatically now.

Since installing this feature, I have now found that I type faster than the answer text box updates. (Note: this is the field I am typing in that updates slowly, not the preview. I could easily ignore it if the preview updated slowly.) I find this more annoying than the feature is helpful.

@Anton: There are a lot of things that can be done to address issues people are having; perhaps the easiest is to have the "live $math$ preview mode" enabled/disabled by a checkbox (it could be tied to a cookie, so the user's choice would persist).

Another approach is to only generate the full preview when the user's input has been idle for more than some amount of time (maybe 1 second)

A slightly more complicated approach is to time how long it takes the preview to generate, and use that number to throttle how often a new preview is generated (i.e. if a user's browser is taking 1 second to generate a preview, then the preview should be generated much less frequently than if their browser could generate the preview in 1ms)

I have no javascript knowledge, but I think danlec's two timing suggestions sound great if they are doable.

Please, please, please turn this off!

I'm working from home on a very fast computer but with only ordinary internet speed (4Mbs) and it is painfully slow.

I would now go so far as to say that this should be off by default. I'm not sure that people are going to realise that it's the preview that is making the site slow and that they can turn it off, and they may just decided that MO is too slow to use (that's one reason why I never use planetmath). Make it easy to turn on, by all means, (and with a warning that it might slow things down), but please, please, please don't have it on by default.

Thank you so much!

@Anton: Sorry this caused so much trouble (in my defense, it was only designed to be used as an "opt-in" scriptlet)

In any case, I've worked out some potential ways of addressing this, and (I think?) I emailed you the details.