propscrub

This extension allows developers to modify properties of elements in the DOM by scrubbing with the cursor.This extension allowed users to easily alter an element's width, height, or font-size by simply scrubbing their cursor across the value. This is a faster way to find values that fit the design you want when making a site (instead of using developer tools and typing in guesses).

Right-click and choose "propscrub" from the context-menu. This activates an "x-ray" vision (similar to chrome developer tools) which lets you isolate elements on the page. Clicking on an element at this stage opens the propscub box. See the big number? Click and drag ("scrub") to alter the property. After that, you can either save the modification (the tick button), undo changes (the middle button), or cancel and close the propscrub box (the cross button).

Happy scrubbing!

(note: this is my first extension so it might be a little buggy - I'd be really grateful if you could send any bugs you find to @sebm90 - thanks!)