This appears to be an e10s problem. I get this series of errors when trying to inject jQuery: Couldn't find Object { text: "jQuery", prefix: " ", suffix: "", _assignment: Object } in Array [ Object ] cli.js:1006 10:46:00.271 Error: Couldn't find jQuery util.js:305 10:46:00.271 "Requisition.prototype.setAssignment@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/gcli/cli.js:1007:1 Tooltip.prototype.fieldChanged@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/gcli/mozui/tooltip.js:196:1 exports.createEvent/event@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/gcli/util/util.js:106:7 SelectionField.prototype.itemClicked/<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/gcli/fields/selection.js:88:1 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 Promise*this.PromiseWalker.scheduleWalkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:744:11 this.PromiseWalker.schedulePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:776:7 Promise.prototype.then@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:451:5 resolve@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/gcli/types/selection.js:160:10 SelectionType.prototype.getLookup@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/gcli/types/selection.js:134:13 SelectionType.prototype.parse@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/gcli/types/selection.js:268:26 exports.items<.parse/conversionPromises<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/gcli/types/union.js:60:16 exports.items<.parse@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/gcli/types/union.js:59:32 SelectionField.prototype.itemClicked@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/gcli/fields/selection.js:87:3 SelectionField.prototype.selectChoice@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/gcli/fields/selection.js:110:1 Tooltip.prototype.selectChoice@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/gcli/mozui/tooltip.js:187:1 Inputter.prototype._handleReturn@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/gcli/mozui/inputter.js:567:8 Inputter.prototype.handleKeyUp@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/gcli/mozui/inputter.js:459:1 Inputter.prototype.onKeyUp@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/gcli/mozui/inputter.js:431:3 EventListener.handleEvent*Inputter@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/gcli/mozui/inputter.js:54:3 DeveloperToolbar.prototype.show/this._showPromise</</</<@resource:///modules/devtools/DeveloperToolbar.jsm:425:27 promise callback*DeveloperToolbar.prototype.show/this._showPromise</</<@resource:///modules/devtools/DeveloperToolbar.jsm:415:16 promise callback*DeveloperToolbar.prototype.show/this._showPromise</<@resource:///modules/devtools/DeveloperToolbar.jsm:412:14 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 Promise*this.PromiseWalker.scheduleWalkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:744:11 this.PromiseWalker.schedulePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:776:7 this.PromiseWalker.completePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:711:7 OutputPanel.prototype._init/onload@resource:///modules/devtools/DeveloperToolbar.jsm:885:5 EventListener.handleEvent*OutputPanel.prototype._init@resource:///modules/devtools/DeveloperToolbar.jsm:887:3 OutputPanel.create@resource:///modules/devtools/DeveloperToolbar.jsm:812:10 DeveloperToolbar.prototype.show/this._showPromise<@resource:///modules/devtools/DeveloperToolbar.jsm:400:7 Handler.prototype.process@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:934:23 Promise*this.PromiseWalker.scheduleWalkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:744:11 this.PromiseWalker.schedulePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:776:7 Promise.prototype.then@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:451:5 DeveloperToolbar.prototype.show@resource:///modules/devtools/DeveloperToolbar.jsm:387:23 DeveloperToolbar.prototype.focusToggle@resource:///modules/devtools/DeveloperToolbar.jsm:364:5 oncommand@chrome://browser/content/browser.xul:1:1 "

Do you still see this issue when using e10s? It appeared to work for me.