The provided link leads to the Mozilla Developer Network (MDN) documentation page, specifically the Japanese version, about Firefox 19. The document outlines various features and improvements made in this browser release.

Here are some key points mentioned on that page:

### New Features and Improvements

* **CSS3 Transforms**: The implementation of CSS3 transforms has been improved.
* **CSS3 Animations**: Support for CSS3 animations has been added.
* **CSS3 Gradients**: Support for CSS3 gradients (linear and radial) is now available.
* **WebGL**: WebGL support in Firefox 19 allows for more sophisticated web-based graphics.
* **WebSockets**: The WebSockets API, which enables bidirectional communication between a web application running in a browser and a server, has been implemented.

### Changes

Some changes are also noted:

* **HTML5 parsing bug fix**: A bug that caused certain HTML5 structures to be incorrectly parsed is fixed.
* **Keyboard event issue**: A problem where the wrong key was fired when pressing the backspace or delete keys on Macs has been resolved.

### Deprecations and Obsoletions

Additionally, it's mentioned:

* **Deprecation of `window.status`**: The `window.status` property, which sets the browser status bar text, is deprecated.
* **Remove support for `line-height` in pixels**: Support for setting the line height to a pixel value has been removed.

### Platform Changes

There are also platform-specific changes mentioned:

* **Mac OS X 10.5 compatibility issue fix**: A bug affecting Firefox's ability to connect to certain servers from Mac OS X 10.5 is fixed.
* **Linux build fixes for Fedora and Ubuntu**

The page provides more detailed information on these topics, including specific code examples, if you're interested in implementing or understanding these features better.

Is there a particular aspect of Firefox 19 that interests you?