I've seen this a handful of times, I believe it's because we don't have a listener on the main GC event from the memory actor when the hook was first implemented (that's not used by the performance tools at all -- we get use the event from a listener on the server side, so this occurs when recording allocations, I believe) console.error: Message: TypeError: this.transport is null Stack: DSC_send@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/server/main.js:1207:5 Actor<._sendEvent@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/server/protocol.js:881:5 Actor<.initialize/<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/server/protocol.js:859:11 emit@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/commonjs/sdk/event/core.js:104:9 MemoryActor<._onGarbageCollection@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/server/actors/memory.js:199:5 emit@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/commonjs/sdk/event/core.js:104:9 MemoryBridge<._onGarbageCollection@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/server/actors/utils/memory-bridge.js:154:5

Haven't seen this in awhile. Closing.