This bug is reproducible on Windows Vista with latest trunk, not with Firefox 2.
The bug still exists on Firefox 3.5.4 on Windows Vista and OSX.
If bug 654072 is fixed, we won't attempt to restore the disabled state, so I guess this will be fixed as well.
Firefox, 50.0a1, Build ID 20160616030228 User Agent Mozilla/5.0 (Windows NT 5.1; rv:50.0) Gecko/20100101 Firefox/50.0 I have tested this issue on the latest Firefox (47.0) release and latest Nightly (50.0a1) build and is no longer reproducible. I have opened the provided test case and after page refresh the "dynamic" button is disabled and the "static" button is active. I can confirm that this issue is reproducible on a older version of Firefox (3.5). After page refresh the both buttons are disabled. Considering this, I will mark this as Resolved-Worksforme. If anyone can still reproduce it, feel free to reopen the issue and provide more information.
I am glad that this bug is now fixed because it was directly or indirectly affecting many websites like youtube.com, https://snapchatonlinelogin.org