With a French Firefox I've got the following error when clicking from the
Preferences item in the menu

"
Erreur d'analyse XML : entité non définie
Emplacement : chrome://buildmonitor/content/prefs.xul
Numéro de ligne 94, Colonne 7 :
<label value="&prefs.hidename;" tooltiptext="&prefs.help.hidename;"/>
"

It seems that there is no entry for prefs.hidename

To be able to work with the version for I've deleted the line
"locale buildmonitor fr-FR jar:chrome/buildmonitor.jar!/locale/fr-FR/"
in the chrome.manifest file