According to the hacks.mozilla website usersnap offers free licenses for foss projects

“We at Usersnap support and believe in the FOSS (Free/Libre and Open Source) movement and that’s why Usersnap is free (as in free beer) for any FOSS project to use.

We utilize a number of open source components like nginx, python, rabbitmq, angular and giving back to the community + improving the quality of your projects is a way to say ???Thanks???

Your project must meet all of the following criteria to be approved:

The project is licensed under a license approved by the Open Source Initiative.
The project source code is available for download.
Your open source project has a publicly accessible website.