I have Thunderbird e-mail client updated to the last version 6.0 and as part of the update routine it checks for compatibility of the add-ons, and it disables the non compatibles ones. This is the exact situation of the bdToolbar 1.0 add-on of Bitdefender in my Thunderbird 6.0, and there is no option for the user to change anything.
I guess there is some hacking that can be done in Thunderbird to force it to enable the add-on, but not knowing the reason of the non-compatibility this does not seems to me the right approach, and most probably will be a waste of time with no good result.
Is this problem known for bdToolbar 1.0 with the new version 6.0 of Thunderbird? If yes I suppose more people with this version of Thunderbird have the same problem. Note: You will be aware of this only if you check the list of add-ons in the Thunderbird add-on manager.