User-Agent Switcher is a quick and easy way to switch between user-agents.
Responsive Web Design Tester
Responsive Web Design Tester is a quick and easy way to test your responsive website.
This extension lets you easy find the most common Opera actions.
Quickly view the HTTP headers of the current tab.
Live HTTP Headers
Monitor all HTTP/HTTPs traffic from your browser.
Whats My Info
Shows your IP address and other useful info.
Base64 Encode and Decode
Quickly Encode & Decode Base64 strings