Can anyone that works at Google tell me what the difference between these two positions are, what I'd be interviewed on, and differences in salary, if any?
I've been given the choice to interview for either. In particular, I'm trying to figure out if "front end" includes native Android or iOS development or if it's strictly web.
"Frontend" at Google is everything from the client (usually Javascript, mobile platforms have their own job titles) back through the webserver and RPC interface to the rest of Google's services. This is somewhat distinct from how the rest of the industry does it; "Frontend SWE" at Google is almost equivalent to "Full Stack Developer" at many startups, because the full server-side code for many startups is like the webserver code for many Google services. It's also why Frontend SWEs need to know at least one server-side language (Java or C++).
The interview process reflects this. When I interviewed, and when I conducted interviews, Frontend SWE candidates usually had 2 interviews that focused specifically on frontend technologies (usually things like Javascript, DOM traversal, web platform APIs, sometimes knowledge of how HTTP works or what your browser is doing when you make a request) and 2 interviews on Gen SWE topics (algorithms, data structures, system design, general programming knowledge).
The Gen SWE position focuses much more on algorithms - Gen SWEs at Google are usually the folks implementing the backend services that the webservers call out to, along with various data pipelines etc. Typically your task is "Design and implement an algorithm to do X, and make sure it runs efficiently", and the interviews reflect this.
When I was there the differences in salary were fairly negligible. I think that Frontend SWEs may have come in with a slightly higher salary & stock grant (though this was an artifact of the times; in 2008 very few devs really knew Javascript well, in 2018 virtually everyone does), but they share the same engineering ladder, so it equalizes over time and your individual job performance matters much more.