Windows and Linux with Firefox: Free Firefox extension CookiePie manages Firefox's cookies—small bits of text stored on your computer that tell a site you're logged in, for example—in such a way that you can log into the same site multiple times. Just right-click a new tab when you want to double-login and toggle CookiePie for that tab. A cookie icon will appear next to the close button and you're
![CookiePie Logs into Multiple Gmail Accounts Simultaneously](https://cdn-ak-scissors.b.st-hatena.com/image/square/d7e6a6f5469cad912e746d908411e51ca810f9c1/height=288;version=1;width=512/https%3A%2F%2Fx.kinja-static.com%2Fassets%2Fimages%2Flogos%2Fplaceholders%2Flifehacker.png)