You can place this one under the “kind of useless but might be of some help to somebody” category. The Tab Counter extension does exactly what you would think. It counts your tabs! After you install it, you get a little number on your toolbar to show exactly how many tabs you have open.
The toolbar’s default position is right before the location bar in the navbar, but you can move it to where ever you want by right clicking on the toolbar and choosing customize and then dragging it anywhere you want.
If you are afraid of having thirteen tabs open – because of the bad luck that might be involved, this extension might be the tool you are looking for.