Amazon says that its Kindle Fire tablet is “the most successful product we’ve ever launched” based on sales. But early adopters have had a mixed reaction to the sometimes jerky graphics, and an off button on the bottom that some users say they frequently hit by accident. The Fire gets a so-so 3.8 stars out of 5 from 3,477 reviewers at consumer electronics site Retrevo — and 4 stars out of 5 from nearly 5,000 reviews on Amazon itself. The online retailer now says it’s on the case: “In less than two weeks, we’re rolling out an over-the-air update to Kindle Fire that will improve performance, touch navigation, and give customers the option to choose what items display on the carousel.” (Nothing they can do about that off button, though.) Consumers shouldn’t be surprised. Our colleagues at BGR.com warned in their review last month that “prospective buyers should expect the occasional hiccup from first-generation software running on $200 hardware. Every computer, smartphone and tablet on the planet stutters from time to time.”