Editors' note, December 12, 2014: Unfortunately, this method for preventing the closure of multiple tabs is no longer effective. This post will be updated when/if that situation changes.
Whether you're researching or adding distractions in other tabs, it can be frustrating when you accidentally close them all at once. For Chrome users, Window Close Protector is an extension that won't win points for creativity for its name, but definitely delivers the ability to prevent you from closing all of your active tabs. This extension mimics the behavior seen when closing a Gmail tab (or similar) during the sending process.
Step 2: Open the Chrome menu by clicking on the wrench icon in at the top of the window. Select Options from the list that appears.
Step 3: In the page that opens, click on Extensions and locate Window Close Protector in the list. Click on the Options link for the extension.
Step 4: Adjust the time options for the extension. Information for what each option does is also displayed in the options window. Click the Save button once your times are set to your liking.
Step 5: Continue browsing normally. When you attempt to close the window, the extension will ask you to confirm that you really want to close. Click Leave this page to close the window.
This extension will hopefully prevent any further browsing accidents from occurring. If you find it too intrusive, try increasing the time values.