How and by what should I create plugin to Firefox?

I'd like to write a plugin for Firefox with the idea of taking HTML code user is presently onto, process it and send it to external php script.

How would you proceed? What programming languages can I use?

How do I add plugins to Firefox?

Click the menu button. , click Add-ons and Themes and select Recommendations. To install a recommended add-on, click the blue + Install Theme or + Add to Firefox button, depending on the type of add-on.

What are Firefox extensions coded in?

Add-ons allow developers to extend and modify the functionality of Firefox. They are written using standard Web technologies - JavaScript, HTML, and CSS - plus some dedicated JavaScript APIs. Among other things, an add-on could: Change the appearance or content of particular websites.

Are there plugins for Firefox?

You can install different types of add-ons, such as extensions to add features to Firefox and themes to change its appearance. Learn more.

There is a wealth of information available online to help you create Firefox extensions.

Here are some good ones: