What is the SOURCEsourceXXX file in firefox debugger and where is it?

i was tried to find some code in website by chrome debugger, but I couldn't find it global search(ctrl+shift+F). so i opened firefox debugger and did samething. then, i saw it exist in SOURCEsourceXXX (XXX is number) file. but i couldn't find this file in source tap and neither network tap. what is this file and where can i find this file?