This week the whole devtools group has been sequestered in Mozilla’s Portland office having one of our regular meet-ups. As always it’s been a fantastically productive week with lots of demos to show for it. I’ll be writing a longer write-up later but I wanted to post about what I played with over the week.

My wife does the odd bit of web development on the side. For a long time she was a loyal Firebug user and a while ago I asked her what she thought of Firefox’s built in devtools. She quickly pointed out a couple of features that Firebug had that Firefox did not. As I was leaving for this week I mentioned I’d be with the devtools group and she asked whether her features had been fixed yet. It turns out that colour swatches had been but the box model still wasn’t editable. So I figured I could earn myself some brownie points by hacking on that this week.

The goal here is to be able to inspect an element on the page, pull up the box model and be able to quickly play with the margins, borders and padding to tweak the positioning until it looks right. Then armed with the right values you can go update your stylesheets. It saves a lot of trial and error with positioning.

It turned out to be relatively simple to implement a pretty full version. The feature allows you to click one of the box model values and type whatever value you like, in any CSS unit you prefer. If the size had been set in the stylesheet in some specific unit then that is what appears in the input box for you to change. Better yet as you type numbers the element updates in the page on the fly and you can use the arrow keys to increase/decrease the value until you’re happy. It’s a really natural way to play with the element’s position.

The changes made appear on the element so you can find them in the rule view pretty easily. This patch is based on an updated version of the box model view which is why it looks so different to existing Firefox, all my work does is make the numbers editable.

I actually completed this so quickly that I decided to take this one step further. One thing missing from the box model display is information about border colours. So I added some colour swatches for each border and made them editable with the regular devtools colour picker.

Both of these patches are pretty much complete but they’ll have to wait for the new box model highlighter to be complete before they can be reviewed and land.