Google allows you the ability to use multiple gmail accounts at the same time through multiple sign-in or email delegation each with their own pros and cons but for me delegation works best because of no limitation of how many email accounts you can have open at once in one browser (multiple sign-in limit is 3 inboxes). The problem with delegation is that you have to login to the first gmail account and then use dropdown menus to open the other accounts.
This tutorial will show you how to easily and quickly open many different gmail accounts in one browser using bookmarks, quick search keywords and keyboard shortcuts inside the Firefox web browser.
This tutorial assumes that you know how to make gmail delegated accounts but if you don't go to this link to find out how.
Once you are logged in (and stay logged in) you can open up delegated accounts from the switch accounts menu or from bookmarks and we'll be using the bookmarks option for this tutorial. The first thing we need to do is login to our Gmail account and then at the top right of the page you can click either your name or your avatar to display a dropdown menu that will allow us to switch accounts.
Once you click the "Switch account" option you will then be presented with a menu that displays all of the available gmail accounts that have been delegated to the account you are logged into.
A new tab or window will load (depending on your personal browser settings) that will contain the inbox of the delegated gmail account.
Once the selected delegated gmail account has been loaded look at the address bar at the top of your browser. Inside the url you will find "/b/XXX/u/" however instead of "XXX" you will find the number value of the particular delegated account inbox. You don't need to do anything with that number, this is to just to show you the difference between the delegated account urls.
The next step is to bookmark this page by pressing Ctrl + D or by doing it from the main "Firefox" menu at the top left of the window. Now you will need to right click the bookmark and select "Properties" on the bookmark you just made. You will find the bookmark in the Bookmarks menu inside the "Firefox" menu, on the Bookmarks Toolbar or by pressing Ctrl + B to open the Bookmarks Sidebar.
In the properties dialog window navigate to the "Keyword" field. There you can put anything you want to use. In the example, I used "gmkey" for gmail keyword but you can use anything that best represents your delegated account or helps you remember the keyword.
Now all you need to do is open a new empty tab by pressing Ctrl + T and type in your new keyword shortcut to open the inbox of the delegated gmail account you just bookmarked.
Now you will be able to use this keyboard / keyword shortcut to easily open delegated gmail accounts by pressing Ctrl + T and then typing in the keyword you used on the account bookmark. If you somehow accidentally leave the address bar (I've done it many times) before typing the keyword press Ctrl + L to quickly put the focus back in the address bar.