This is a further commitment to supporting Firefox on the part of Yahoo, who began their support with a search toolbar for Firefox, released last month. However, it has been discovered that many users reverted back to IE when they were unable to use many Yahoo features with Firefox. Yahoo has now promised to change all that.
"Due to the explosive popularity of the Firefox browser, it has now been added to our suite of browsers to test our products against. All new products that Yahoo develops will be tested against Firefox." - Yahoo spokesperson.