▶ IMPORTANT To have this Userstyle fully Usable:
read: https://forum.userstyles.org/discussion/53510/x
Cf the Parmeters screenshot

NEW : Style Updated for all these Perpetual NEW DESIGNS:
- Oct 2014
- May 2015
- June 2015 (Date Label in Mails List).
TESTED only on Firefox :
If Good On Other Browser :
SAY it to me !

This Style clean all Pubs / ADDS but you can too use :
▶ This greasemonkey script:
http://userscripts-mirror.org/scripts/show/3115
▶ Remove Message "ADD Yahoo for MAILTO" :
http://forums.mozillazine.org/viewtopic.php?f=38&t=2820341

Note for ADBlock:
I use it with EsyList filter and that's OK on one profile but not on an other (???) .....
Solution:
If you have a problem on the Mails list view ,
watch if you have this rule enable and disable it:

mail.yahoo.com##div[id^="yui_"][role="presentation"] > div[id][class][aria-hidden]

▶ SCROLLBARS :
For Slims and Dark ScrollBars , i use My Userstyles :
http://freestyler.ws/style/125810/slim-dark-scrollbar-firefox

It is a tweak of:
▷ http://freestyler.ws/style/124176/scrollbars-slim-arrowless
You can test too :
▷ http://freestyler.ws/style/101886/fx-scrollbars-adjustments

▷ LAST changes :
- Settings pages
- Top Search / Search in Mail Corrections
- ADD USERSTYLES: "Yahoo Mail Wide Messages List" by "120591"
- YAHOO NAVBAR Hidden (Visible on Hover the "Plus"/"More" button.
- TOP HEADER improve style
>> Images sizes sent by Mail : less wide (max-wide) and mozaic view