Make Observer.localizationsByRoot a WeakMap
Make Observer.localizationsByRoot a WeakMap

projectfluent/fluent.js,zbraniecki/fluent.js,zbraniecki/l20n.js,projectfluent/fluent.js,l20n/l20n.js,stasm/l20n.js,projectfluent/fluent.js,zbraniecki/fluent.js