The car analogy starts to fall apart when you are talking about something that continues to get updates. Sure, they release new versions of cars usually every year, but you are buying an entirely new car, not really updating your old one.

It also starts to fall apart when talking about price. You can talk about browsers costing time, effort, privacy, etc, but this isn't the same as talking about thousands of actual dollars.

> real extensions

Unless I'm mistaken, I don't believe Firefox is going to have those for too much longer: https://blog.mozilla.org/addons/2015/08/21/the-future-of-dev...