Browser extensions tend to inject CSS/JS into every webpage your visit. A cleaner approach is to use bookmarklets. Simply add the snippets below as bookmarks and access them from your bookmark/address bar.
Bookmarklet / Bookmarklet with Login Fix
javascript:window.open('https://getpocket.com/edit?url='+document.location,'PocketAdd','height=360,width=600')
javascript:void((function(d){var%20e=d.createElement('script');e.setAttribute('type','text/javascript');e.setAttribute('charset','UTF-8');e.setAttribute('src','//assets.pinterest.com/js/pinmarklet.js?r='+Math.random()*99999999);d.body.appendChild(e)})(document));
javascript:location.href='https://pushtokindle.fivefilters.org/send.php?url='+encodeURIComponent(document.location.href);