I have Adobe XI Standard and when I create a PDF from a web page in FireFox v 52.7.2, the PDF is blank.
Sorry for the delayed response and inconvenience caused. AS per the description above, when you are creating a PDF from a webpage using Acrobat standard 11 on Firefox browser, the PDF comes blank, Is that correct?
Please check for any pending updates of Acrobat from help>check for updates, reboot the machine after installing any updates and see if this brings any difference.
Try creating the PDF from Acrobat itself from File>Create>Web page and see if the PDF is still blank.
Try using a different browser like Chrome and create the PDF from the webpage and see if the issue is reproducible.
Under the Advanced Settings in File>Create>Web page, check the conversion settings.
You can also refer to Converting web pages to PDF, Adobe Acrobat
Note: Acrobat 11 is already declared as an End of support product, End of Support means that Adobe no longer provides technical support or distributes runtimes. This policy affects product and security updates for all derivatives of a product or product version (localized versions, minor upgrades, operating systems, dot and double-dot releases, and connector products).
For detailed information, please refer to End of support for Adobe Acrobat XI and Reader XI
Let us know how it goes and share your findings.