Not really, you just happened to pick two projects that are particularly large and particularly old. Drive-by commits are a lot less valuable in those type of projects, unfortunately, but you can still find places to contribute if you spend the time to look.
While I did pick the projects for their notability, I could point out the fact that Gnome have an active disdain for extension developers and the entire idea of extensions as well as Mozilla continuing to make unpopular decision after unpopular decision with their browser.
