FF search settings error

A coding exception was thrown and uncaught in a Task.

Full message: TypeError: engine is null
Full stack: this.ContentSearch._currentEngineObj<@resource:///modules/ContentSearch.jsm:461:9
TaskImpl_run@resource://gre/modules/Task.jsm:314:40
TaskImpl@resource://gre/modules/Task.jsm:275:3
createAsyncFunction/asyncFunction@resource://gre/modules/Task.jsm:249:14
this.ContentSearch._currentStateObj<@resource:///modules/ContentSearch.jsm:442:28
TaskImpl_run@resource://gre/modules/Task.jsm:314:40
TaskImpl@resource://gre/modules/Task.jsm:275:3
createAsyncFunction/asyncFunction@resource://gre/modules/Task.jsm:249:14
this.ContentSearch._onMessageGetState@resource:///modules/ContentSearch.jsm:221:12
this.ContentSearch._onMessage<@resource:///modules/ContentSearch.jsm:215:13
TaskImpl_run@resource://gre/modules/Task.jsm:314:40
Handler.prototype.process@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:934:23
this.PromiseWalker.walkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:813:7
this.PromiseWalker.scheduleWalkerLoop/<@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:747:1