This can be a good thing that it allows you to preview the website that you would visit from the search result and avoid the dodgy ones. The thumbnail image is quite clear to preview the page.
The downside of this addon is that this could be a bandwidth hog especially if you are browsing from a low speed connection.
This addon is supposed to work on Bing to show the thumbnail preview but as far as I can see this is not the case. To support my claim, the options for SearchPreview only has Google and Yahoo on it and not Bing.
Overall a nice neat addon for those who need it.
The addon works on Firefox 1.5 to 3.6b1pre. To install the addon, click here from a Firefox browser and click Install. Once installed, restart Firefox.
Click here to visit the project home.