Pick Sort File Tabs Alphabetically from the Go menu to sort the tabs of all files in the current project alphabetically by their file names. Note that the tabs will be sorted only at the moment you click on Sort File Tabs Alphabetically. If you open more files, the alphabetical order will not be maintained. Tabs for newly opened files are either placed to the immediate right hand side of the tab that was active when you opened the additional files, or after the last file tab. You can configure this in the Tabs Preferences.
You can also rearrange the tabs in any order you want by dragging them with the mouse. To drag a tab, click on it, hold the mouse button down, and move the mouse to the left or right. The tab will follow the mouse pointer until you release the mouse button. If you drag the tab to the left edge of the leftmost tab, and there are more tabs, presently invisible, to the left of that tab, then all the tabs will scroll to the right, allowing you to move the tab you are dragging further to the left. Similarly, you can drag the tab to the right edge of the rightmost tab to make the tabs scroll to the left.
Go|Sort Project Tabs Alphabetically