Since CS6 is now "end-of-life" and no longer officially supported by Adobe, using unofficial serial numbers or pirated versions carries a high risk of malware, and the software itself may not run reliably on modern operating systems [1, 2, 4].
If you previously purchased a physical or digital copy of CS6, you can retrieve your registered serial number by logging into your Adobe Account under the "Products" tab. 3. Modern Free & Paid Alternatives adobe fireworks cs6 serial number free