I ran into a problem caused by a internal site setting invalid cookies (ones with “@” as part of the cookie name) and tried to fix it by using the Firefox cookie manager to delete the offending cookie. This might have been OK, except that I’d also set Firefox to not allow a site for which I’d removed cookies to set cookies in the future.
And so removing the one errant cookie blocked all ibm.com sites from setting cookies — this had some unfortunate side effects (such as making it impossible to log into several internal sites). I couldn’t find any way to reverse this, either — not even running Firefox in safe mode helped.
So I resorted to rummaging through my profile directory and looking at any file which was human-readable. The last file I checked (of course!) was hostperm.1; that file had a line in it setting the “cookie” property of ibm.com to “2”. I deleted the line and my problems went away.
I will probably keep the Firefox setting to prohibit a site who’s cookies I’ve deleted from setting cookies in the future, but this posting will help me remember what to do if it causes me problems, too.