I take pride in my ability to pixel-match my UX to a designer's mocks.
XScope is my preferred toolkit for mock matching. It's been a standby for my since I discovered it in 2012.
I do a lot of dev on a custom Win10 box that I built a few years back, and XScope is NOT Win10-compatible.
Pixels is a Chrome Extension that replicates some of my favorite XScope functionality in the browser.
Pixels relies on full control of the browser window through Chrome's extension APIs.
Everything worked great in local development, but I ran into permissions problems as soon as I tried to publish to Chrome's Extensions store.
I abandoned the project. The core extension code still works "ok", but I couldn't achieve a smooth install process.