I loved this extension until recently when the latest update comepletely broke it so it's making my browser crash everytime I try to use it.I've had to disable it since the new patch started closing my browser down.I'm on Firefox v56 on the 64 bit install and that's what started crashing after this new update.
It was working fine on my other 32 bit install of Friefox v39 so I might see if downgrading to that one might help.

amazing

rất hữu hiệu

Good add on for web developers, a classic add-on for Firefox.

I only wanted to use display window size and change size but they aren't working in developer edition :(

A classic and very useful addon. For those using a FF browser with XUL support; the version 2.0.3 works fine in Waterfox (FF56) whereas v1.2.13 works in Basilisk (FF52)

Web Developer includes CSS tools, forms tools, HTML/CSS validation tools, & more. I recommend this extension for web developers.

good word. a very helpful tool

My go to developer tool in Firefox and Chrome. Reliable, easy to use, able to inspect element in Responsive design and see how changes will look. Almost perfect (if the inspector could show these changes across all screen sizes, this would give it 10 stars)