Several profiles problems with both FF and TB - MozillaZine Forums
Thunderbird2 has tag functionality. However, the UI is not good enough. Methods to add tags are annoying if you have many tags. Attached tags are difficult to recognize. Tag Toolbar facilitates the tag functionality.
“Seek†adds faceted browsing features to Mozilla Thunderbird and lets you search through your email more effectively.
Integrating Firefox and Thunderbird into KDE