You could inspect the source code and build it yourself (about 300 lines of JavaScript + JQuery): https://github.com/prashantbaid/scrolltrotter
Installation of software will always require a leap of faith that the publisher doesn't have ill intent.
Views the source code straight from the google store
It'd be great if chrome and firefox allowed open source chrome extensions to be compared with their git source tree, possibly with diffs between releases.
Still, though, how many people will go through that effort?