The 3D view is not "every day" useful, but people have found it to be a quick way to spot unexpected nesting issues.
As noted elsewhere, this feature started life as an add-on made during Google Summer of Code 2011 by Victor Porof, who continues to work on Firefox developer tools today.
(in case you hadn't guessed, I work for Mozilla... usual biases therefore apply ;)
It's apparently very useful for discovering some nasty XSS bugs. I think eventually, this might be one of the "last stops" in testing new front-end designs; a staple, but not something you need to be switching into every five minutes (unless there's something to be fixed.)
Very jealous of this as a Chrome user. :) Good job guys.
It was the most awesome thing in my talk at HOPE Number 9 about using browser tools to figure out what sites are doing. I compared it with the scene in Jurassic Park where the girl "knows Unix".
Cool. To see it, turn on inspector (right-click page, inspect element) and on the info bar at the bottom is a "3D View" button. Try both mouse buttons and the mouse wheel.
Too bad they didn't put some inertia in it, it would be fun to flick around the webpage.
I am a bit baffled by the switch from your 2010 scenario myself. Many people were obsessed with semantic markup, but now things like bootstrap.css come along that clearly violate that idea and I don't hear a peep about it.
Some people reconcile it by saying bootstrap is (as the name implies) just for getting things up and running and once your site is stable you should switch to better markup. But I don't think anyone actually does that.
It has been out for awhile, but it seems like a lot of people weren't aware of the feature. One additional usage - introduce non-programmers/web designers to what is really behind what they see on a webpage. Most people find the 3D view pretty cool, no matter if they're a technical person or not. It's also been great to see the FF developer tools improve so much recently.
Not very useful, but a cool effect. Life is much better when we can host web browser instances as textures. Geometry (as in this case) would allow for even better effects; I feel bad that I never thought of that!
It's been around as an addon for a while, I think it was put into FF at version 11 (March 2012). I really think it should have remained as an extension, it looks neat but is pretty useless.
I opened a long page, tilted a little, reached the end, and pressed the down button to scroll the page up. Heavens! It's like watching the first scene of Star Wars.
It also makes pages with a billion wrapper divs look much thicker! Therefore I use it to get an impression of the weight/awkwardness of the DOM of a page.
Nice feature but poor UI (controls) for me. Zoom (mousewheel) and rotate (left click) should take place around the cursor (or the 3d space it is currently hovering over) rather than the centre of the screen. Makes things much easier for the user (especially the power-user, who this is aimed at and can spare the 30-seconds to figure out how it works).
As an extra, clicking the mousewheel down should allow you to 'pan' (rather than 'rotate' on mouse1)...
i use something similar for WPF called Snoop. these types of things are also useful when you're trying to see the complexity or optimize the nesting levels of your controls.
You have to open the inspector first (Ctrl+Shift+I or Firefox->Web Developer->Inspector), and then click the "3D" button on the bottom left (or bottom right if you're on some beta/nightlies).
http://blog.mozilla.org/blog/2012/03/13/firefox-adds-new-dev...
The 3D view is not "every day" useful, but people have found it to be a quick way to spot unexpected nesting issues.
As noted elsewhere, this feature started life as an add-on made during Google Summer of Code 2011 by Victor Porof, who continues to work on Firefox developer tools today.
(in case you hadn't guessed, I work for Mozilla... usual biases therefore apply ;)