A script that allows to download HorribleSubs shows using Seedr.cc service just by clicking on Magnet/Torrent links.

horribleSeedrLinkr.js

// ==UserScript==
// @name         HorribleSubs to Seedr Linker
// @description  A script that allows to download HorribleSubs shows using Seedr.cc service just by clicking on Magnet/Torrent links.
// @author       Manciuszz
// @version      0.2
// @require      https://cdnjs.cloudflare.com/ajax/libs/babel-standalone/6.18.2/babel.js
// @require      https://cdnjs.cloudflare.com/ajax/libs/babel-polyfill/6.16.0/polyfill.js
// @require      https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.slim.min.js
// @match        https://horriblesubs.info/shows/*
// @match        https://www.seedr.cc/files*
// @grant        GM_notification
// @grant        GM_getTabs
// @grant        GM_openInTab
// @grant        GM_saveTab
// @grant        GM_addValueChangeListener
// @grant        GM_deleteValue
// @grant        GM_setValue
// ==/UserScript==

var inline_src = (<><![CDATA[
    "use strict";

    (function() {
        let waitForEl = function(selector, callback) {
            if (jQuery(selector).length) {
                callback();
            } else {
                setTimeout(function() {
                    waitForEl(selector, callback);
                }, 100);
            }
        };

        let horribleSubsFunc = function() {
            GM_saveTab({tab: "horriblesubs.info"});
            let bindTriggersToLinks = function() {
                jQuery('a[title="Magnet Link"], a[title="Torrent Link"]').on('click', function(evt) {
                    evt.preventDefault();
                    let link = this.href;
                    checkForTabs(function(tabStatus) {
                        if (tabStatus == "closed") {
                            GM_openInTab("https://www.seedr.cc/files", { active: false });
                            let dropTorrentsId = setInterval(function() {
                                checkForTabs(function(tabStatus) {
                                    if (tabStatus === "opened") {
                                        GM_setValue("droppedTorrent", link);
                                        clearInterval(dropTorrentsId);
                                    }
                                });
                            }, 250);
                        }
                    });
                    GM_setValue("droppedTorrent", link);
                });
            };
            let checkForTabs = function(callbackFn) {
                GM_getTabs(function(tabObjects) {
                    if (!Object.values(tabObjects).map( (val, index) => val.tab).includes("seedr.cc")) {
                        if (typeof callbackFn === "function")
                            callbackFn("closed");
                        else
                            GM_notification({title: 'Linking HorribleSubs to Seedr.', text: 'Please login to Seedr.cc service.'});
                    } else {
                        if (typeof callbackFn === "function")
                            callbackFn("opened");
                        else
                            GM_notification({title: 'Linked HorribleSubs to Seedr', text: 'Click on magnet or torrent links to start uploading...'});
                    }
                });
            };
            waitForEl('a[title="Magnet Link"]', function() {
                bindTriggersToLinks();
                checkForTabs();
            });
        };

        let seedrFunc = function() {
            GM_deleteValue("droppedTorrent");
            GM_saveTab({tab: "seedr.cc"});

            let startUploading = function() {
                jQuery("#upload-button").click();
            };

            let inputSeedr = function(link) {
                jQuery('input[type=text]',"#link-upload-text").val(link);
                setTimeout(startUploading, 0);
            };

            !function bindListener() {
                GM_addValueChangeListener("droppedTorrent", function(name, old_value, new_value, remote) { // Updates only on a NEW VALUE
                    if (new_value)
                        inputSeedr(new_value);
                    GM_deleteValue("droppedTorrent");
                });
                GM_notification({title: 'Seedr Listening to HorribleSubs...', text: 'Waiting for torrents...'});
            }();
        };

        let main = ({"www.seedr.cc": seedrFunc, "horriblesubs.info": horribleSubsFunc})[location.host]();
    })();
]]></>).toString();
var c = Babel.transform(inline_src, { presets: [ "es2015", "es2016" ] });
eval(c.code);