How do Gmail plugins such as Rapportive work?

I know Gmail has contextual and side-bar gadgets, but how do browser extensions such as Rap开发者_JAVA百科portive 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?

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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.

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