What is fireurl?

[colons]

I think it'd be nice to have at least a sentence at the top of the readme that says, in brief, what this project is trying to do.

In netblue30/firejail#5364, you discuss what 'Level 0' and 'Level 1' are specifically (although it does not define 'unlocked'). Levels 2 and 3 are links to things that have a readme and comment that explain what they do pretty thoroughly. But here, there's a readme that just says 'Fixing the firejail URL open issue.', and then talks about how to build it and some implementation details. It takes some digging to learn what 'the firejail URL open issue' even is.

Maybe I'm missing something obvious here, but I don't know how to learn what fireurl actually is. What are its design goals, what is its security model, and how does it present itself to users?