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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