hi, the browser you are using doesn't have any influence on the windows 10 upgrade offer. please contact microsoft's support forum instead if you want to seek help about that issue: http://go.microsoft.com/fwlink/p/?LinkId=528873

No, using firefox doesn't change your eligibility for Windows 10. Certain machines manufacturers haven't decided to support windows 10, meaning the upgrade is disabled. You can work around that but I'm not going to tell you how since it can break your computer. Call a local IT store to get it done.

sam7755 said

I tried to update my Windows 7 at Microsoft for the free Windows 10, but was told I'm not eligible.

http://www.microsoft.com/en-ca/windows/windows-10-upgrade Windows 10 Upgrade Offer is valid for qualified Windows 7 and Windows 8.1 devices, including devices you already own. Some hardware/software requirements apply and feature availability may vary by device and market. ... Some editions are excluded: Windows 7 Enterprise, Windows 8/8.1 Enterprise, and Windows RT/RT 8.1. ... To check for compatibility and other important installation information, visit your device manufacturer’s website and the Windows 10 Specifications page.