How to write a browser plugin?

I'm curious as to the procedure for writing browser plugins for browsers like Chrome, Safari, and Opera. I'm thinking specifically of Windows here and would prefer working with C++.

Are there any tools or tutorials that detail the process?

Note: I am not referring to extensions or 'addons'. I'm referring to a plugin similar to how Flash and Adobe Reader have plugins to handle specific content-types.

As others point out, plugins for those browser are written using the NPAPI.

Note: Both Firefox and Chrome will default most plugins to click-to-play soon, with Chrome planning to phase out NPAPI entirely. NPAPI for new projects is discouraged at this point.

Resources for getting started with NPAPI:

• MDC plugin section
• three part NPAPI tutorial
• memory management in NPAPI
• npsimple - the "Hello World" of NPAPI plugins
• npapi-sdk - the source for the canonical NPAPI headers
• Mozillas test plugin - good for looking up specific NPAPI use cases

The NPAPI itself is however relatively low-level, but there are tools and frameworks that can help you with it:

• FireBreath - cross-browser, cross-platform frame-work for plugins
• Nixysa - generate glue-code for NPAPI plugins
• JUCE - application framework also providing support for plugins
• QtBrowserPlugin - Qt based browser plugin framework