With a lot of tabs open, it can be difficult to keep track of those really important ones like your email and calendar tabs. Try “pinning” those tabs to keep them first and foremost in your tab bar.
In Chrome, just right-click the tab and select “Pin tab.” The tab will move to the left of all other tabs and will no longer have a close icon. If you need to unpin or close a pinned tab, just right-click it again and select “Unpin tab” or “Close tab” as appropriate. The steps are nearly identical for Firefox.