InvCounter

This extension, when clicked, will show you the exact inventory count for various stores. These stores include shop.funko.com, hottopic, boxlunch, target, and various emp domains.

This is useful for helping you determine when/if you should buy a specific item. Sometimes, you might want to hold off on purchasing an item until you can use a coupon code or combine it with other items to save on shipping. But if the quantity remaining is low, then you might want to purchase the item right away.

When using, be sure to be on a specific product page and not the home page. For example, when on the funko shop, be sure to click the item's title to be taken to the specific product page as sometimes the homepage can LOOK like a product page but it is actually just the home page.

For the funko shop, this extension uses the bisection method to determine the inventory count of items as the specific count is not exposed. Instead, it makes a series of intelligent guesses until it determines the correct number. You can follow along with this process as the extension will change text on screen to show you what number it is guessing at the time.

For assistance, message u/RegExr on Reddit.