Browser extension
Install Bookmer from the store for the browser you use, then sign in with the same Bookmer ID as on the website.
Chrome, Brave, Vivaldi, and Yandex use the Chrome Web Store listing. Microsoft Edge uses Edge Add-ons. Firefox uses Firefox Add-ons. Safari on Mac uses the Bookmer Safari extension. Turn it on under Safari, Settings, Extensions.
Use the toolbar button on the page you want to keep. The website still works with no extension. The extension is the faster way to save the tab you already have open.