How do Gmail plugins such as Rapportive work?

Question

I know Gmail has contextual and side-bar gadgets, but how do browser extensions such as Rapportive work? Are they injecting their buttons / displays into the browser page? If so, wouldn't the browser extension break if Google decided to change the way they layout the page?

Answer 1

Are they injecting their buttons / displays into the browser page?

Yes.

If so, wouldn't the browser extension break if Google decided to change the way they layout the page?

Probably.

Answer 2

The probably leverage some part of the Gmail Greasemonkey API and inject scripts into the page to use this.