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Introducing the "Cross-Browser" Browser (Freeware)
Site Inspector is a Web browser that combines the two most frequently used browser engines (Internet Explorer and Mozilla/Gecko) into one program. Its advanced web page analysis features make it the perfect companion for webmasters and web developers.
With Site Inspector’s very own browser, the Analyzing Browser, users can switch between the two browser engines with just one mouse click, e.g., to compare the rendering of a page in both browsers. The sophisticated web page analysis functions - which also integrate into Internet Explorer and Firefox - make analyzing and debugging web sites easy.
more and download: Paessler Site Inspector