The id's as unique user id's are currently not secure. You can impersonate any other id by changing the value in local storage in the browser. If you have logs see 5f2860 and fb86f7
OSX was used originally to just describe version 10, a big change to the OS which broke backwards compatibility. Now its used loosely to describe any version above 9.
Each point version of OSX has a codename, Yosemite is v10.10.
The latest version 10.14.x has the name Mojave.
Apple recently rebranded OSX to macOS, possibly to have a version number higher than 10 some day.
"The only exception to the foregoing is scripts and code downloaded and run by Apple's built-in WebKit framework or JavascriptCore, provided that such scripts and code do not change the primary purpose of the Application by providing features or functionality that are inconsistent with the intended and advertised purpose of the Application as submitted to the App Store."