書き込み欄上部（モバイル版ではタブバー）にアカウント表示ボタンを追加します。新規リストに表示させたいアカウントを追加して、リスト番号を指定してください。

mastodon_profile_shortcut.user.js

// ==UserScript==
// @name        [Mastodon] profile shortcut
// @namespace   hen.acho.co
// @include     https://*/web/*
// @version     1.220302
// @description jump to your favorite account easily
// @downloadURL https://gist.github.com/pacochi/ca65a42509080210ddb12ec650fbe995/raw/mastodon_profile_shortcut.user.js
// @run-at      document-idle
// @grant       none
// ==/UserScript==

// 監視対象が一定しないので雑に五秒後につけることにした
setTimeout((() => {

	let profileListId = localStorage.getItem('profileListId');
	const accessToken = JSON.parse(
	 (document.querySelector('#initial-state') || {}
	).textContent || '{ "meta": {} }').meta.access_token;
	// 自分が使ってない機能のとこ置き換えてる

	if (!accessToken) return;

	const E = (name, attr = {}) => Object.assign(document.createElement(name), attr);

	if (!document.getElementById('profile-shortcut-css')) document.head.appendChild(
	 E('style', { id: 'profile-shortcut-css', textContent: `
.tabs-bar {
	overflow: visible;
}
.profile-shortcut {
	position: relative;
	display: block;
	width: 40px;
	height: 40px;
	min-height: 40px;
	line-height: 40px;
	z-index: 0;
	text-align: center;
	margin: -12px auto -10px auto;
}
.navigation-bar .profile-shortcut {
	margin: 0;
}
.profile-shortcut .profile-shortcut-icons{
	display: none;
	position: absolute;
	top: 40px;
	left: 0;
	width: 40px;
}
.profile-shortcut:focus-within {
	z-index: 4;
}
.profile-shortcut:focus-within .profile-shortcut-icons {
	display: block;
}
.profile-shortcut-icon {
	width: 40px;
	height: 40px;
	background-size: 40px 40px;
	cursor: pointer;
	border: 0;
	margin: 0;
	padding: 0;
}
.profile-shortcut-setting {
	color: #fff;
	background-color: transparent;
	cursor: pointer;
	border: 0;
	margin: 0;
	padding: 0;
}
`
	 })
	);

	// https://gist.github.com/unarist/a5998d24c5bcb207376ab22c05f24e5c からもらってきた
	const getHistory = () => {

		const rootContainer = document.getElementById('mastodon')._reactRootContainer;
		let current_node = (rootContainer._internalRoot || rootContainer).current.child;

		while (current_node) {

			const history = current_node.memoizedProps.history;
			if (history) return history;
			current_node = current_node.child;

		}

	};


	const changedLink = document.querySelector('[data-preview-title-id="pawoo.column.suggested_accounts"], [data-preview-title-id="column.public"], [data-preview-title-id="column.community"]');
	const fromPC = !document.querySelector('.columns-area__panels') || getComputedStyle(document.querySelector('.tabs-bar') || {})?.display == 'none';
	const parentElm = fromPC ? document.querySelector('.navigation-bar')
	 : E('strong', { className: 'tabs-bar__link' });

	if (!parentElm) console.log('[profile-shortcut] no parentElm', fromPC);
	if (!fromPC && changedLink) changedLink.replaceWith(parentElm);

	const container = parentElm.appendChild(E('strong', { className: 'profile-shortcut' }));
	const setting = container.appendChild(E('button', {
	 className: 'profile-shortcut-setting'
	}));
	const settingIcon = setting.appendChild(E('i', { className: 'fa fa-fw fa-plus-square' }));
	const icons = container.appendChild(E('span', { className: 'profile-shortcut-icons' }));

	const addIcon = account => {

		const icon = icons.appendChild(E('button', {
		 style: `background-image: url('${account.avatar}');`,
		 className: 'profile-shortcut-icon',
		 title: account.acct
		}));

		icon.addEventListener('click', e => {

			getHistory().push('/accounts/' + account.id); // + '/with_replies');
			e.target.blur();
			e.preventDefault();

		});

	};

	const getProfiles = profileListId => {

		if (!profileListId || !accessToken) return;

		const profileEndpoint = `/api/v1/lists/${profileListId}/accounts?limit=0`;

		document.querySelectorAll('.profile-shortcut-icon').forEach(icon => icon.remove());
		settingIcon.className = 'fa fa-fw fa-heart';

		fetch(profileEndpoint, {
		 headers: { Authorization: 'Bearer ' + accessToken } 
		}).then(r => r.json()).then(json => json.forEach(account => addIcon(account)));

	};

	setting.addEventListener('contextmenu', e => {

		profileListId = parseInt(prompt('リストの ID', ''));
		if (profileListId) localStorage.setItem('profileListId', profileListId);
		getProfiles(profileListId);
		e.preventDefault();

	});

	getProfiles(profileListId);

}), 5000);