HTTP Header Plugin od Paul Pepper

"Add HTTP Header" lets you define rules that automatically inject or override HTTP request headers on outgoing network requests.

Features:
• Add new headers or override existing ones for matching requests
• Three URL matching modes: Contains (simple substring), Wildcard (* and ?), and Regular Expression
• Rules take effect immediately — no browser restart needed
• Clean options page to add, edit, and delete rules
• Privacy policy displayed directly in the Options UI

How it works:
The extension listens to outgoing requests via the webRequest API. When a request URL matches one of your configured rules, the specified header is added or updated before the request is sent. All rules are stored in your browser's local storage and never transmitted anywhere.