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Web Developer 1.1.8 Build June 30, 2009
According to the developers site it's the latest: http://chrispederick.com/work/web-developer/
Don't you have the whole Tools section, or just this one option? Tools is actually just a bunch of links that use the current url as a querystring, just go to "Edit tools" and at this to it (Tool type URL):
Also, Firebug & YSlow are imho superior in helping you reduce page size and page speed, which is I assume you're up to since this is in SEO. Do some Google searches for those and you should find some tutorials on this matter.