Assorted List of Productivity Boosters for Firefox users (without plugins). These tips are for everyone.

  1. Use middle-click on your mouse to open a link in new tab.
  2. Use middle-click on your mouse on a tab to close it.
  3. You can set all the open tabs as your homepage set. Whenever you open your browser they can be set to automatically open in tabs. This is a way to open all your important pages at the same time.
  4. To save all the open tabs as a folder press Ctrl-D and select to save all the tabs in a folder. You can choose your folder.
  5. Additionally you can select any bookmarked folder and open all the pages as tabs by right-clicking on it and selecting - "Open in tabs".
  6. Use Ctrl + to increase font size.
  7. Use Ctrl - to decrease font size.

Any more comes to your mind (without using plugins)?

Check Firefox article for tips which involve modifying text files to add them, in other words not for basic users.