This feature was added for US users in December 2014 and manifests itself as a red blinking number in the top left tab navigation.
Here's something that worked for me, using Adblock Plus 2.6.6 and Firefox 34.0.5 on Windows 8.1. YMMV.
- Make sure Adblock is enabled for Yahoo! Mail. (I had it disabled, because I use the ad-free paid subscription.)
- From the Adblock icon, open "Filter preferences" (Ctrl+Shift+F).
- Go to "Custom filters" and add a new filter group ("Add filter group"). I named it "Personal Rules", since I plan to use more of those in the future.
- Add a new filter ("Add filter") to that group. Enter
mail.yahoo.com###newsfeed-openeras the filter rule. Make sure it's "Enabled" (should be automatical).
- Close the Adblock Plus Filter Preferences, then reload Yahoo! Mail.
Please let me know whether this works for you.
This solution was inspired by a Techdows post, though it didn't work for me exactly as described there.
I just had success now with Ad Blocker Plus. I have Windows 7 and Chrome. We went into the ABP stop sign icon on the upper right corner of the page. Once there, we chose "block element" When you select this, text or elements you pass over with your mouse will be brightly highlighted. Go to the Yahoo news feed. Light it up and confirm "block element". Success.