Mozilla is investigating reports that Dell is charging users with new computers to install the Firefox browser.
One user told the Register website that he had been asked to pay £16.25 to have the browser installed.
Firefox is a free, open-source piece of software that can be installed by anyone in about 10 minutes.
Mozilla said there was "no agreement" with Dell that would allow it to charge for installing Firefox.
"Our trademark policy makes clear that this is not permitted and we are investigating this specific report," said Denelle Dixon-Thayer, vice-president of Mozilla's general counsel.
In Mozilla's policy document on that, it clearly states: "If you are using the Mozilla Mark(s) for the unaltered binaries you are distributing, you may not charge for that product.
"By not charging, we mean the Mozilla product must be without cost and its distribution (whether by download or other media) may not be subject to a fee, or tied to subscribing to or purchasing a service, or the collection of personal information."
In response Dell said that the money was being charged for the time and labour involved.
"In this particular situation, the customer would not be charged for the Mozilla Firefox software download, rather the fee would cover the time and labour involved for factory personnel to load a different image than is provided on the system's standard configuration."
There was anger on Twitter about the row.
"Shame on @DellUK for selling @Firefox to customers," said one.
Another commented: "That's £100 per hour to install free software."
Firefox has proved to be a popular browser. It reported that, at the end of 2013, it had half a billion users around the world on desktop computers and another 50 million on Android.