Sam Ramji, director of Microsoft's Open Source Software Lab, sent an email to a Mozilla development mailing list offering access to the Windows Vista Readiness lab in December.
The Vista Readiness lab on Microsoft's campus allows developers to test applications for potential compatibility issues. Microsoft engineers will be available to provide one-on-one support if needed.
"In the past [Microsoft] has only invited commercial software developers to these labs," Ramji wrote in his email.
"I am committed to evolving our thinking beyond commercial companies to include open source projects, so I went to the non-trivial effort of getting slots for non-commercial open source projects."
A Microsoft spokesman confirmed the email's authenticity to vnunet.com.
Firefox has chipped away at Internet Explorer's market share in recent years and currently runs on nearly 13 per cent of the world's computers, according to data from Onestat.
Thunderbird is an email and news client developed by the Mozilla Corporation.
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iTnews Executive Retreat - Security Leaders Edition
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