This script adds some extra controls to EBay search result pages.
The control group that is added allows you to display a secondary result pager at the top of the results column, re-order results so that they are listed from low to high price, hide sponsored item listings and open an individual item result in a new tab/window. In addition, and the primary use of this script (IMO), it is capable of blocking sellers by removing their items from your list of search results. Items sold by sellers in your block list are hidden by default, but the script gives an option of displaying a placeholder for each one. It also adds the ability to easily block any seller by simply clicking on the red "X" icon that is inserted into the result details.
To get the most out of this script, it's recommended to ensure that item results also display the seller information. You can set that up by going to "View" and then "Customize", from any EBay search result page. Simply tick the box marked "Seller information".
The script is also fully supported in Chrome, with TamperMonkey.
UPDATE [10/14/2017]: With the release of FireFox 57, I suggest switching from GreaseMonkey to TamperFox, if you haven't already done so. This script is fully supported. I also suggest that you export your blocked seller list before you update to FireFox 57 - you'll loose your list, if you don't!