Interesting project and very curious how they even get it to build. They use Firefox ESR and compile it with lots of optimizations and maaaany redundant configs. I chatted with developers in the FF Matrix about that, they build firefox with 2 arguments or so, build browser, use official branding.
Many things are duplicate and mercury may be unstable because of that.
The biggest problem is that it doesnt use a CI/CD workflow, so that dude does the builds manually and you can hope to get them in time. And them they are distributed as Appimages, which is a different set of problems