SearchPreview is a free plugin for Firefox. When you do any search on Google, Yahoo, or Bing, SearchPreview adds thumbnails of websites to your search results. In this way, you do not need to visit every website in your search result to check it out, and really speed up the process of narrowing down to what you require.
SearchPreview was earlier known as GooglePreview. It is exceptionally fast, and does not deteriorates the performance of search results. The reason for this is that SearchPreview serves the images from its dedicated servers, so it does not have to generate them on fly. SearchPreview uses the Webshot tool to take images of whole webpages.
SearchPreview sometimes inserts Sponsored links also with search results, but it clearly marks them as such. You can easily disable those in settings if you do not want those. Also, if you do not want SearchPreview to show images, you can turn it off very easily.
SearchPreview is really good, extremely easy, and a great free tool. I also recommend that you some type of link scanner tool, like AVG Linkscanner Free, that can warn you about any malicious website in your search results before you visit that.