re-logging in manually isn't what I'd call dealing with it.
Firefox 4:
Tools menu, pick Options
Privacy tab, pick "remove individual cookies"
search for thefiringline
Chrome:
From the main menu (wrench icon top right to the right of the url bar), pick Options (windows) or Preferences (linux).
On the left pane, pick "Under the Hood"
At the top, pick "Content Settings ..."
Near the top, pick "All cookies and site data"
search for thefiringline
Look at all cookies starting with "bb". The domain for each bb* cookie should be ".thefiringline.com"
If you see any cookies with domain* thefiringline.com (without a leading dot), remove them.
*Do not confuse the "Site" column in Firefox's and Chrome's listings with the domain. In FF the domain is shown near the bottom when you highlight a particular cookie -- you should see "Name:", "Content:", "Domain:" series of values on sequential lines. In Chrome, when you click on a cookie to view, you should see a similar "Name:", "Content:", "Domain:" list of values pop up below the cookie list.
Obviously, if you don't care about having to log in again, you can delete all cookies from thefiringline.com and then the cookie problem should be sorted.
A similar exercise can be applied to any forum site you're having trouble with. You only need to know what domain they set cookies for, and delete any possibly conflicting cookies with different domains. If you visit a site foo.com, the cookies that get sent are foo.com and .foo.com. If you visit a site
www.foo.com, the cookies that get sent are
www.foo.com and .foo.com