Pressto,
Please open Firefox and go to the TOOLS menu (it's default location is the top left menu unless you've customized it) and select OPTIONS.
When the Options menu appears you should see something similar to this:
Click the PRIVACY tab and take a look at the section I've circled red. Do your settings match the ones in the picture above? If they don't, please match the settings above, click the OK button, restart Firefox and try to login again.
If they do match, please click the EXCEPTIONS button. When the exception list comes up please make sure that WGT.COM is NOT listed as Blocked. If it is listed as Blocked click on WGT.COM and then click the REMOVE SITE button, then click CLOSE. Click OK one final time to close the options and restart Firefox.