This paper is about Europe and thus does not shed much light on al-Majriti. The paper is about a metaphysical principle, not an empirical one. People point to al-Majriti because he might have done relevant experiments.
After thousands of years of acceptance of this metaphysical principle, Occam was skeptical; perhaps the original application of his razor was that "quantity of matter" was meaningless, and thus too its conservation (though atomists could use a count). Later 14th century Europeans defined "quantity" as "mass," and thus made a precise claim. Following Averroes, they used inertial mass, not gravitational mass.
So you could say that Lavoisier did not discover conservation of mass, but experimentally checked it. But he made a big splash at the time, probably because scientists were no longer so enthusiastic about metaphysical speculation. In particular, he showed the 14th century people made the right guess.
One of the sharpest and most important tools in the LessWrong cognitive toolkit is the idea of going meta, also called seeking whence or jumping out of the system, all terms crafted by Douglas Hofstadter. Though popularized by Hofstadter and repeatedly emphasized by Eliezer in posts like "Lost Purposes" and "Taboo Your Words", Wikipedia indicates that similar ideas have been around in philosophy since at least Anaximander in the form of the Principle of Sufficient Reason (PSR). I think it'd be only appropriate to seek whence this idea of seeking whence, taking a history of ideas perspective. I'd also like analyses of where the theme shows up and why it's appealing and so on, since again it seems pretty important to LessWrong epistemology. Topics that I'd like to see discussed are: