SearchPreview is a simple Chrome, Firefox and Safari add-on which extends search pages with thumbnail previews, related links and popularity ratings.
Supported search engines include Google, Bing, Yahoo and DuckDuckGo.
SearchPreview worked as advertised for us, with no noticeable drop in browsing performance on our desktop. The extra overhead may slow you down a little on mobile devices, but the thumbnail file sizes are small (4-5KB each, typically 50KB in total per page) and unlikely to make any real difference.
One potential issue is that the add-on may display ads amongst its "related links". The developer makes this clear in his description and the interface, though, and you can disable the "related links" feature entirely if you prefer.
This is the version for Firefox.
SearchPreview is easy to use, and the preview thumbnails really can make it quicker and easier to scan through a page of search results for the links you need.