In Firefox, when you click a bookmark, it replaces the current page. To open it in a new tab, you need to press Ctrl while clicking the bookmark. I think a bookmark should open in a new tab just by clicking. I just found an extension that does exactly that.
The extension also enables you to re-open a tab that you closed but on a second thought you regret that you did. Actually, it can reopen the last 10 tabs, or more if you set it to.
Get the click2tab extension from here
شفت مفاجأة النهاردة ؟ اضغط هنا عشان تشوفها (مفاجأة جديدة كل يوم)