--- a/devtools/client/framework/toolbox.js
+++ b/devtools/client/framework/toolbox.js
@@ -1643,18 +1643,16 @@ Toolbox.prototype = {
     }
 
     if (!this.hasAdditionalTool(toolId)) {
       throw new Error("Tool definition not registered to this toolbox: " +
                       toolId);
     }
 
     this.additionalToolDefinitions.delete(toolId);
-    this.visibleAdditionalTools = this.visibleAdditionalTools
-                                      .filter(id => id !== toolId);
     this.unloadTool(toolId);
   },
 
   /**
    * Ensure the tool with the given id is loaded.
    *
    * @param {string} id
    *        The id of the tool to load.
@@ -2469,31 +2467,61 @@ Toolbox.prototype = {
 
     // Select another tool.
     if (this.currentToolId == toolId) {
       let index = this.panelDefinitions.findIndex(({id}) => id === toolId);
       let nextTool = this.panelDefinitions[index + 1];
       let previousTool = this.panelDefinitions[index - 1];
       let toolNameToSelect;
 
+      // If the toolId can't be found in the globally registered panel definitions
+      // Check if the tool was actually part of the additional tools created by
+      // a WebExtension.
+      if (index === -1) {
+        let additionalNextTool;
+        let additionalPrevtool;
+
+        let additionalToolIndex = this.visibleAdditionalTools
+                                      .findIndex(id => id === toolId);
+
+        if (additionalToolIndex >= 0) {
+          additionalNextTool = this.visibleAdditionalTools[additionalToolIndex + 1];
+          additionalPrevtool = this.visibleAdditionalTools[additionalToolIndex - 1];
+
+          if (!additionalPrevtool) {
+            previousTool = this.panelDefinitions[this.panelDefinitions.length - 1];
+          }
+        }
+
+        if (additionalNextTool) {
+          nextTool = additionalNextTool;
+        }
+
+        if (additionalPrevtool) {
+          previousTool = additionalPrevtool;
+        }
+      }
+
       if (nextTool) {
         toolNameToSelect = nextTool.id;
       }
       if (previousTool) {
         toolNameToSelect = previousTool.id;
       }
+
       if (toolNameToSelect) {
         this.selectTool(toolNameToSelect);
       }
     }
 
     // Remove this tool from the current panel definitions.
-    this.panelDefinitions = this.panelDefinitions.filter(({id}) => id !== toolId);
     this.visibleAdditionalTools = this.visibleAdditionalTools
                                       .filter(id => id !== toolId);
+    this.panelDefinitions = this.panelDefinitions.filter(({id}) => id !== toolId);
+
     this._combineAndSortPanelDefinitions();
 
     if (panel) {
       panel.remove();
     }
 
     if (this.hostType == Toolbox.HostType.WINDOW) {
       let doc = this.win.parent.document;