The open nature of the web is being threatened by the spread of media plug-ins from Adobe and Microsoft, according to Tristan Nitot, founder of the Mozilla open source browser.

Applications such as Flash and Silverlight are being offered for free, but could give their creators an unfairly dominant position of control, he claimed.

“You are producing content for your users and there is someone in the middle deciding whether users should see your content,” said Nitot in a speech at the Internet World exhibition in London last week.

“If Adobe or Microsoft decide to compete with you, and you’re using their technology, you cannot compete.”

Microsoft and Adobe could use this to limit the activities of competitors, and both companies have a history of removing or reducing their support for third-party browsers, claimed Nitot.

He told delegates Microsoft no longer produces Internet Explorer for Mac or Unix systems, and that Adobe has been slow to update its Linux-compatible version of Flash.

While tools such as these play an important role in supporting multimedia content, this task will soon be handled by HTML 5, the next revision of the programming language used across the web.

In the meantime, Nitot warned, businesses should be wary of the free tools offered by the industry’s biggest names. “They’re not here for the glory; they’re here for the money,” he said.

“If you consider proprietary technologies, think hard; are you really trading convenience in the short term with independence in the long term?”