I'm not sure what has happened, but all of a sudden, the WebExtension I am working on started to throw an error when debugging. So far as I'm aware, there was no change to the code to cause the error, and I even rolled back to an earlier version of the extension in order to see if I had inadvertently caused a problem by adding something to the scripts I couldn't remember adding. The earlier version is no longer working correctly either. Everything seems to be find until I add a breakpoint. After adding a breakpoint to the debugger in the FireFox Developer browser, an error is thrown, and I am unable to step through the code. Previously, I was able to set breakpoints and step through normally, but it will not work any longer. I've searched for answers online, but I'm not able to understand the error enough to gain any traction. Here is the error the console is writing: error occurred while processing 'frames: TypeError: window is null Stack: webExtensionChildPrototype.isExtensionWindow@resource://devtools/shared/base-loader.js -> resource://devtools/server/actors/webextension.js:284:3 webExtensionChildPrototype._allowSource@resource://devtools/shared/base-loader.js -> resource://devtools/server/actors/webextension.js:304:13 TabSources/this.allowSource@resource://devtools/shared/base-loader.js -> resource://devtools/server/actors/utils/TabSources.js:30:39 source@resource://devtools/shared/base-loader.js -> resource://devtools/server/actors/utils/TabSources.js:118:12 createNonSourceMappedActor@resource://devtools/shared/base-loader.js -> resource://devtools/server/actors/utils/TabSources.js:357:12 getFrameLocation@resource://devtools/shared/base-loader.js -> resource://devtools/server/actors/utils/TabSources.js:587:7 form@resource://devtools/shared/base-loader.js -> resource://devtools/server/actors/frame.js:93:31 onFrames@resource://devtools/shared/base-loader.js -> resource://devtools/server/actors/thread.js:949:18 onPacket@resource://devtools/shared/base-loader.js -> resource://devtools/server/main.js:1761:15 receiveMessage@resource://devtools/shared/base-loader.js -> resource://devtools/shared/transport/transport.js:735:7 enter@resource://devtools/shared/base-loader.js -> resource://devtools/server/actors/utils/event-loop.js:118:5 _pushThreadPause@resource://devtools/shared/base-loader.js -> resource://devtools/server/actors/thread.js:178:5 _pauseAndRespond@resource://devtools/shared/base-loader.js -> resource://devtools/server/actors/thread.js:390:7 hit@resource://devtools/shared/base-loader.js -> resource://devtools/server/actors/breakpoint.js:188:12 appAPI.CallCrossDomain@moz-extension://d059ac7f-1fe3-7649-b7ca-e14cb93b87b0/popup/scripts/appapiclass.js:92:8 CheckLoginProcess@moz-extension://d059ac7f-1fe3-7649-b7ca-e14cb93b87b0/popup/scripts/popup.js:1434:4 FireLogin@moz-extension://d059ac7f-1fe3-7649-b7ca-e14cb93b87b0/popup/scripts/popup.js:1632:5 DrawLoginUI/<@moz-extension://d059ac7f-1fe3-7649-b7ca-e14cb93b87b0/popup/scripts/popup.js:181:6 dispatch@moz-extension://d059ac7f-1fe3-7649-b7ca-e14cb93b87b0/popup/scripts/jquery.js:5182:16 add/elemData.handle@moz-extension://d059ac7f-1fe3-7649-b7ca-e14cb93b87b0/popup/scripts/jquery.js:4991:6 Line: 284, column: 3 main.js:1616 _unknownError resource://devtools/server/main.js:1616:5 onPacket resource://devtools/server/main.js:1764:29 receiveMessage resource://devtools/shared/transport/transport.js:735:7 enter resource://devtools/server/actors/utils/event-loop.js:118:5 enter self-hosted:981:17 _pushThreadPause resource://devtools/server/actors/thread.js:178:5 _pauseAndRespond resource://devtools/server/actors/thread.js:390:7 next self-hosted:1219:9 hit resource://devtools/server/actors/breakpoint.js:188:12 appAPI.CallCrossDomain moz-extension://d059ac7f-1fe3-7649-b7ca-e14cb93b87b0/popup/scripts/appapiclass.js:92:8 CheckLoginProcess moz-extension://d059ac7f-1fe3-7649-b7ca-e14cb93b87b0/popup/scripts/popup.js:1434:4 FireLogin moz-extension://d059ac7f-1fe3-7649-b7ca-e14cb93b87b0/popup/scripts/popup.js:1632:5 DrawLoginUI/< moz-extension://d059ac7f-1fe3-7649-b7ca-e14cb93b87b0/popup/scripts/popup.js:181:6 dispatch moz-extension://d059ac7f-1fe3-7649-b7ca-e14cb93b87b0/popup/scripts/jquery.js:5182:16 add/elemData.handle moz-extension://d059ac7f-1fe3-7649-b7ca-e14cb93b87b0/popup/scripts/jquery.js:4991:6 I can provide code snippets if needed, but since the error is only thrown after I add the breakpoint, I don't know what code would be helpful for leading to a solution. I'm hoping I have not missed something silly here, but I have searched for "window is null", "TypeError: window is null", "'frames: TypeError: windows is null" as well as other debugging searches in relation to jQuery and just can't find anything. Any help would be much appreciated.