A panel of mobile phone users found that Amazon’s new Kindle Fire tablet has an error-prone browser, a touchscreen too small for fingers and an overall "poor" user experience.

A study from the Nielsen Norman Group – which was conducted among four test participants with between 1.5 and 2.5 years of experience using touchscreen devices – found that usability on the Kindle Fire isn’t as seamless as promised. Although the test group is small, Nielsen noted that qualitative studies often generate deeper feedback than bigger studies that are more focused on metrics. Half of the test group own Android phones and the other half use iPhones.

“The most striking observation from testing the Fire is that everything is much too small on the screen, leading to frequent tap errors and accidental activation,” said Nielsen Normal Group founder Jakob Nielsen, who also participated in the study along with the four other individuals.

He noted that one participant spent a few minutes attempting to log in to Facebook, but kept pressing the wrong text field. This was on a page with only two text fields and one button.

In addition to experiencing errors with the Kindle Fire’s "Silk" browser – calling it clunky and unreliable – participants expressed concern with how sites were displayed on its 7-inch screen. Previous studies conducted by Nielsen Normal Group found that full sites work well on 10-inch tablets such as the iPad and specialized mobile sites are superior on smaller touchscreens that are 3.5-inch diagonal. However, the test group said the Kindle Fire isn’t best optimized for either of these platforms.

"Using designs intended for a full screen on a 7-inch tablet is like squeezing a size-10 person into a size-7 suit,” Nielsen said. “Accessing full desktop sites on the Fire was a prescription for failure in our testing. Users did much better when using mobile sites."

Participants said sites optimized for 3.5-inch mobile screens felt “luxurious” on the Kindle Fire, likening it to accessing a regular site on an extra-large computer monitor.

Meanwhile, the group favored the traditional Kindle design when it came to reading books, but agreed that the Kindle Fire was tops for graphic-rich magazines. However, it noted that its screen has more glare than the traditional Kindle device.

Other complaints from the group include that the Fire is too heavy and that it takes a while for pages to load.

Despite such concerns, Amazon's new tablet is selling well. Last week it unseated the iPad as the best-selling tablet at Best Buy and researcher IHS iSuppli predicts Amazon will sell 3.9 million Kindle Fires before the end of the year.