Your English is perfect. There is no indication of low intelligence from the way you described your issues. B and C grade are pretty average and indicates you can learn with hard work. I think what you might be experiencing is anxiety and that is causing you to think you don’t have skills or intelligence. I am not from US so I don’t know what kind of help might be available for you there, but I would suggest you to look for a job with something you like to do even though the pay might not be great and then eventually your interest will take you further in your career.

FSF does not get in the way of security. FSF believes source code should be publicly available in order to even assume the software is secure or private. In a perfect world that would be nice. But in the real world, proprietary blobs are required to make the hardware functional. As long as OEMs are removed about open sourcing the firmwares, both GrapheneOS and GNU are right in their own way.

Yep. It was developed to improve parallelization and security of Firefox. Many core parts of Firefox have been replaced with Rust implementations.