I have not been able to login on the Admin Console of WLS 8.1 with Internet Explorer 6.0 or Firefox 1.0.7, but, my IE&FF always gives me the following message:
"The Weblogic Server administration console requires that browsers support session cookies. Please update the browser configuration and try again."
For IE, I went to Tools-->Internet Options-->Privacy-->Advanced->Checked the "Override automatic cookie handling"--->checked on "Always allow session cookies". Then deleted the previous cookies,deleted offline content. And clicked on "Sign In" button again. But again its showing me the same error.