Visbug is an amazing new browser extension that allows you to do a visual inspection of your website in development.

What they have to say about their tool and capabilities

Point, click & tinker
Edit or style any page, in any state, like it’s an artboard
Hover inspect styles, accessibility and alignment
Nitpick layouts & content, in the real end environment, at any device size
Leverage adobe/sketch skills
Edit any text, replace any image (hi there copywriters, ux writers, pms)
Design within the chaos: use production or prototypes and the odd states they produce, as artboards and design opportunities
Design while simulating latency, i18n, media queries, platform constraints, CPUs, screensize, etc
Make more decisions on the front end of your site/app (a11y, responsive, edge cases, etc)
No waiting for developers to expose their legos, just go direct and edit the end state (regardless of framework) and execute/test an idea

For Designers & Content Creators

A really nice tool for designers & content creators, helping them to optimize the look and feel of a website.

The extension is currently available for Chrome, but a Firefox Addon is in development.