Incompatibility with "Folder Pane View Switcher" add-on
FPVS cannot work with MNP. I consider it as minor bug in FPVS. I.e. it cannot use Log4Moz module if it is used by others already. I cannot be 100% sure, but it looks that like variable scoping issue. Simple move of one line of code in FPVS fixes the situation. Here is fixed version of FPVS: FolderPaneSwitcher@kamens.us.xpi Save it as file and install through "Thunderbird->Add-on Manager->Install from file"