Mozilla has launched a new initiative called Contributions that encourages users to contribute money to Firefox Add-on developers.
The payments will go through PayPal. Developers will be able to create a PayPal ID for each of their Firefox Add-ons, while users will see a “Contribute” button on the Add-on pages through which they can make a payment. The amount is not fixed: developers can suggest an amount, but the contributors may choose to pay a different amount of money. Together with this initiative, Mozilla has also introduced "About the Developer" pages, where the developers can write something about themselves and perhaps better explain their mission to the users.
Mozilla calls this initiative a "pilot" feature. From the FAQ:
"For this pilot, Mozilla will not earn a percentage of any contributions made by users. Developers will receive all the proceeds from contributions minus the PayPal transaction fee."