One of the most important concepts in web site design is something called CSS, or Cascading Style Sheets. They allow the design and layout of the site (fonts, colours, positions on the page) to be defined somewhere other than alongside the content itself (the text and pictures).
For the web site designers and programmers, this makes it much easier to manage things, because the textual content resides in one file and the style definitions are in another one.
"Stylish" is a free add-in for Firefox and Chrome that intercepts the communication between a web site and its CSS file, ie its list of style definitions, and allows you to change those styles. At one level, this means that you can re-skin your favourite web site just by downloading Stylish and then adding in the new style definitions for whatever site you choose.
But styling a page doesn't just mean picking its font and colour. Style definitions also allow you to hide things. And so one of the style definitions available for Stylish is designed to hide Promoted Tweets (otherwise known as adverts), to stop them appearing in your feed.
To get started with Stylish, which is free, head to https://addons.mozilla.org/en-US/firefox/addon/stylish/?src=external-use... for Firefox or https://chrome.google.com/webstore/detail/fjnbnpbmkenffdnngjfgmeleoegfcffe for Chrome. Once installed in your browser, browse to the site you want to style and then click the Stylish icon to search for available skins.