- A-Grade browsers get full support. Yahoo does extensive testing, and tries to make services work well in them.
- C-Grade browsers are known to have problems, and get sent "lowest-common denominator" code. When last checked, the only C-Grade browser was IE 5.0.
- X-Grade browsers are everything else. They get the same code as A-Grade browsers, but Yahoo doesn't do any testing on them.
A few months ago, they added Opera 9 on Windows XP to their A-Grade list (replacing Opera 8).
This time around, they've made several interesting changes:
- Expanded A-list support for Opera 9 across all operating systems they support, including Mac OS and older Windows releases.
- Added IE7 and Firefox 2 to the A-list.
- Dropped IE 5.5 and Firefox 1.0 from A-list to X-list.
- Dropped Netscape from A-list to X-list.
The first item is most significant for Opera users, because it brings Yahoo's official policy on Opera support up to the same level as their support for Firefox.
The new chart only shows A-grade browsers, so it's not clear whether IE 5.0 is still supported at C-grade level or dropped to X-grade like IE 5.5. This may reflect support at Microsoft, which maintains support for IE 5.0 on Windows 2000, but not IE 5.5. You can't even download IE 5.5 from Microsoft anymore. You can get IE 5.0 by installing Windows 2000, and you can update to IE6 or download the installer, but you can't update to or download IE 5.5.
The fact that they've dropped Netscape is interesting, and represents another nail in the coffin of the web's former dominant player. Of course, the real action moved from Netscape to Mozilla years ago.