Search Engine Results are filled with Duplicate Content created from Wikipedia Dumps. They add little or no relevance to the results and may even highjack the original Wiki content page.So here's a simple way to filter sites from Google search result pages which mirror Wikimedia content:
1. Install the CustomizeGoogle extension for Firefox
2 Save this site-list file on your machine
3. In CustomizeGoogle options, choose Filter tab -> Import button
4. Locate the file you saved and select it
5. Click OK
Source: Mirror filter from Meta
Wikipedia:Mirrors and forks | Copyright Issues | Download Wikipedia
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