This tool is good and it works well too. The only thing that is somewhat of a concern is the impression that the developer is not really satisfied with all the 5 stars rating, the nice reviews and having over 80k users.
One of the posts on the developers homepage: "Google and Mozilla are failing to support browser extension developers" - clearly spells out that he is not getting any profit, or enough profit.
And it goes on with further complaining: "Accepting such an offer may significantly improve one’s life, and it can be potentially life-changing. It feels like a just reward for all those years of free labor, and it’s uplifting for someone to value your work and propose to buy your project."
"Mozilla has deprioritized the placement of the donation button during the redesign of Firefox Add-ons. The button was pushed below the fold, previously it was featured prominently near the install button. Requesting donations at the end of the install flow has also been deprecated."
Here he is complaining about that Mozilla did redesign AMO. While the new design made the donation button less in your face, the developer is obviously not pleased with this new design.
He also shows examples of people who is contacting him and making a business propose. Another hint rubbing into our face that he get offers to sell his extensions but have no done that. (in other words, people contacting me offering me money for my extensions) a guilt trip for not getting enough donations from the users.
Conclusion, the fact that one of the extensions (Search by image) has getting the recommended status by Mozilla, all the nice reviews, all the 5 stars and all the 82k users that most likely will increase each day, is not enough for him. He is, between the lines, bitter and complaining that he do not get any money from us, or at least, not enough donations.
There are plenty open source developers out there who is not that hungry for money. There are open source developers who choose to not have that contribute button even.