What are the best options for performing Web Scraping of a not currently open tab from within a Google Chrome Extension with JavaScript and whatever more te
If you are fine looking at something beyond a Google Chrome Plugin, look at phantomjs which uses Qt-Webkit in background and runs just like a browser incuding making ajax requests. You can call it a headless browser as it doesn't display the output on a screen and can quitely work in background while you are doing other stuff. If you want, you can export out images, pdf out of the pages it fetches. It provides JS interface to load pages, clicking on buttons etc much like you have in a browser. You can also inject custom JS for example jQuery on any of the pages you want to scrape and use it to access the dom and export out desired data. As its using Webkit its rendering behaviour is exactly like Google Chrome.
Another option would be to use Aptana Jaxer which is based on Mozilla Engine and is very good concept in itself. It can be used as a simple scraping tool as well.