WebAssembly is disabled in the Firefox 52 Extended Support Release (ESR), the last version for WinXP.

https://developer.mozilla.org/en-US/docs/WebAssembly see Browser compatibility about halfway down that page.

Thank you for the information. Unfortunately I have no idea how to apply this information to my computer so I no longer have this issue. What I do not understand is I have been using the offending website for months with no issues. Then I hit my bookmark and I get this WebAssembly notice. I am running Windows 7 so why would this affect me if it is no longer supporting WinXP?

You posted with a Firefox 52.0 user agent on Windows XP.

• User Agent: Mozilla/5.0 (Windows NT 5.1; WOW64; rv:52.0) Gecko/20100101 Firefox/52.0

You can check that you do not run Firefox in compatibility mode. You can open the Properties of the Firefox desktop shortcut via the right-click context menu and check the "Compatibility" tab. Make sure that all items are deselected in the "Compatibility" tab of the Properties window.

Sorry but this information did not resolve my issue. I still get the same error message when I try to open the website I have been using for months. Two days ago my computer suddenly stopped accessing the site and leaving me with the error message: Uncaught Exception: WebAssembly support not detected in this browser. What happened???

Are you possibly using "Resist Fingerprinting" in Firefox or have an extension that modifies how Firefox reports itself?

• https://support.mozilla.org/en-US/kb/firefox-protection-against-fingerprinting

I have made no changes to my computer between the time I was accessing the website and when I started receiving the error message that I can no longer access that site. I have no idea what "fingerprinting" means.

Please verify that you are in fact using Firefox 52 on the Windows XP operating system.

And if not, you need to check the desktop shortcut that your use to open Firefox; in the Compatibility tab of the Properties window for that shortcut, make sure that Run this program in the compatibility mode for Windows XP (SP3) is not selected.

And that might explain why your problem is transitory; if Firefox is opened via an external link by the operating system, that desktop shortcut option wouldn't come into play.

I have no idea if I am using Firefox 52 on the Windows XP operating system. How would I determine that?

Also, I have unchecked "Run this program in the compatibility mode for Windows XP (SP3)" so it is not selected.

Did not make any difference. Again, I am trying to open a website, not run a program. I have been using this website for months. I am suspecting that Firefox has made changes to its browser program and that Is why it no longer opens the website. Is there a way to use a previous edition of Firefox that was allowing me to function on that website?

Yes I am running Firefox version 52.9.0, 32-bit. My OS is Windows XP although computer says I am running on Windows 7