diff --git a/accessible/field.component.js b/accessible/field.component.js
index 93a058857..7affe7e53 100644
--- a/accessible/field.component.js
+++ b/accessible/field.component.js
@@ -30,11 +30,13 @@ blocklyApp.FieldComponent = ng.core
     template: `
     <input *ngIf="isTextInput()" [id]="mainFieldId" type="text" [disabled]="disabled"
            [ngModel]="field.getValue()" (ngModelChange)="field.setValue($event)"
-           [attr.aria-label]="disabled ? 'Disabled text field' : 'Press Enter to edit text'">
+           [attr.aria-label]="disabled ? 'Disabled text field' : 'Press Enter to edit text'"
+           tabindex="-1">
 
     <input *ngIf="isNumberInput()" [id]="mainFieldId" type="number" [disabled]="disabled"
            [ngModel]="field.getValue()" (ngModelChange)="field.setValue($event)"
-           [attr.aria-label]="disabled ? 'Disabled number field' : 'Press Enter to edit number'">
+           [attr.aria-label]="disabled ? 'Disabled number field' : 'Press Enter to edit number'"
+           tabindex="-1">
 
     <div *ngIf="isDropdown()"
          [attr.aria-labelledBy]="generateAriaLabelledByAttr('blockly-argument-menu', idMap['label'])">
@@ -43,7 +45,7 @@ blocklyApp.FieldComponent = ng.core
         <li [id]="idMap[optionValue]" role="treeitem" *ngFor="#optionValue of getOptions()"
             [attr.aria-labelledBy]="generateAriaLabelledByAttr(idMap[optionValue + 'Button'], 'blockly-button')">
           <button [id]="idMap[optionValue + 'Button']" (click)="handleDropdownChange(field, optionValue)"
-                  [disabled]="disabled">
+                  [disabled]="disabled" tabindex="-1">
             {{optionText[optionValue]}}
           </button>
         </li>
diff --git a/accessible/toolbox-tree.component.js b/accessible/toolbox-tree.component.js
index 0bd31ac8f..e5bbb75be 100644
--- a/accessible/toolbox-tree.component.js
+++ b/accessible/toolbox-tree.component.js
@@ -37,14 +37,14 @@ blocklyApp.ToolboxTreeComponent = ng.core
         <li [id]="idMap['workspaceCopy']" role="treeitem"
             [attr.aria-labelledBy]="generateAriaLabelledByAttr(idMap['workspaceCopyButton'], 'blockly-button')"
             [attr.aria-level]="level + 2">
-          <button [id]="idMap['workspaceCopyButton']" (click)="copyToWorkspace()">
+          <button [id]="idMap['workspaceCopyButton']" (click)="copyToWorkspace()" tabindex="-1">
             {{'COPY_TO_WORKSPACE'|translate}}
           </button>
         </li>
         <li [id]="idMap['blockCopy']" role="treeitem"
             [attr.aria-labelledBy]="generateAriaLabelledByAttr(idMap['blockCopyButton'], 'blockly-button')"
             [attr.aria-level]="level + 2">
-          <button [id]="idMap['blockCopyButton']" (click)="copyToClipboard()">
+          <button [id]="idMap['blockCopyButton']" (click)="copyToClipboard()" tabindex="-1">
             {{'COPY_TO_CLIPBOARD'|translate}}
           </button>
         </li>
@@ -52,7 +52,7 @@ blocklyApp.ToolboxTreeComponent = ng.core
             [attr.aria-labelledBy]="generateAriaLabelledByAttr(idMap['sendToSelectedButton'], 'blockly-button', !canBeCopiedToMarkedConnection())"
             [attr.aria-level]="level + 2">
           <button [id]="idMap['sendToSelectedButton']" (click)="copyToMarkedSpot()"
-                  [disabled]="!canBeCopiedToMarkedConnection()">
+                  [disabled]="!canBeCopiedToMarkedConnection()" tabindex="-1">
             {{'COPY_TO_MARKED_SPOT'|translate}}
           </button>
         </li>
diff --git a/accessible/toolbox.component.js b/accessible/toolbox.component.js
index a20d6c152..a7d5acd93 100644
--- a/accessible/toolbox.component.js
+++ b/accessible/toolbox.component.js
@@ -30,7 +30,7 @@ blocklyApp.ToolboxComponent = ng.core
       <h3 #toolboxTitle id="blockly-toolbox-title">Toolbox</h3>
       <ol #tree
           id="blockly-toolbox-tree" role="tree" class="blocklyTree"
-          *ngIf="toolboxCategories && toolboxCategories.length > 0" tabIndex="0"
+          *ngIf="toolboxCategories && toolboxCategories.length > 0" tabindex="0"
           [attr.aria-labelledby]="toolboxTitle.id"
           [attr.aria-activedescendant]="getActiveDescId()"
           (keydown)="treeService.onKeypress($event, tree)">
diff --git a/accessible/tree.service.js b/accessible/tree.service.js
index ec175649c..0c463e191 100644
--- a/accessible/tree.service.js
+++ b/accessible/tree.service.js
@@ -82,21 +82,19 @@ blocklyApp.TreeService = ng.core
       }
       return null;
     },
-    focusOnNextTree_: function(treeId) {
+    getIdOfNextTree_: function(treeId) {
       var trees = this.getAllTreeNodes_();
       for (var i = 0; i < trees.length - 1; i++) {
         if (trees[i].id == treeId) {
-          trees[i + 1].focus();
           return trees[i + 1].id;
         }
       }
       return null;
     },
-    focusOnPreviousTree_: function(treeId) {
+    getIdOfPreviousTree_: function(treeId) {
       var trees = this.getAllTreeNodes_();
       for (var i = trees.length - 1; i > 0; i--) {
         if (trees[i].id == treeId) {
-          trees[i - 1].focus();
           return trees[i - 1].id;
         }
       }
@@ -190,12 +188,11 @@ blocklyApp.TreeService = ng.core
       if (e.keyCode == 9) {
         // Tab key.
         var destinationTreeId =
-            e.shiftKey ? this.focusOnPreviousTree_(treeId) :
-            this.focusOnNextTree_(treeId);
-        this.notifyUserAboutCurrentTree_(destinationTreeId);
-
-        e.preventDefault();
-        e.stopPropagation();
+            e.shiftKey ? this.getIdOfPreviousTree_(treeId) :
+            this.getIdOfNextTree_(treeId);
+        if (destinationTreeId) {
+          this.notifyUserAboutCurrentTree_(destinationTreeId);
+        }
       }
     },
     isButtonOrFieldNode_: function(node) {
@@ -260,16 +257,20 @@ blocklyApp.TreeService = ng.core
           // For Esc and Tab keys, the focus is removed from the input field.
           this.focusOnCurrentTree_(treeId);
 
-          // In addition, for Tab keys, the user tabs to the previous/next tree.
           if (e.keyCode == 9) {
             var destinationTreeId =
-                e.shiftKey ? this.focusOnPreviousTree_(treeId) :
-                this.focusOnNextTree_(treeId);
-            this.notifyUserAboutCurrentTree_(destinationTreeId);
+                e.shiftKey ? this.getIdOfPreviousTree_(treeId) :
+                this.getIdOfNextTree_(treeId);
+            if (destinationTreeId) {
+              this.notifyUserAboutCurrentTree_(destinationTreeId);
+            }
           }
 
-          e.preventDefault();
-          e.stopPropagation();
+          // Allow Tab keypresses to go through.
+          if (e.keyCode == 27) {
+            e.preventDefault();
+            e.stopPropagation();
+          }
         }
       } else {
         // Outside an input field, Enter, Tab and navigation keys are all
@@ -302,14 +303,14 @@ blocklyApp.TreeService = ng.core
             }
           }
         } else if (e.keyCode == 9) {
-          // Tab key.
+          // Tab key. Note that allowing the event to propagate through is
+          // intentional.
           var destinationTreeId =
-              e.shiftKey ? this.focusOnPreviousTree_(treeId) :
-              this.focusOnNextTree_(treeId);
-          this.notifyUserAboutCurrentTree_(destinationTreeId);
-
-          e.preventDefault();
-          e.stopPropagation();
+              e.shiftKey ? this.getIdOfPreviousTree_(treeId) :
+              this.getIdOfNextTree_(treeId);
+          if (destinationTreeId) {
+            this.notifyUserAboutCurrentTree_(destinationTreeId);
+          }
         } else if (e.keyCode >= 35 && e.keyCode <= 40) {
           // End, home, and arrow keys.
           if (e.keyCode == 35) {
diff --git a/accessible/workspace-tree.component.js b/accessible/workspace-tree.component.js
index 39e33b048..b024101d6 100644
--- a/accessible/workspace-tree.component.js
+++ b/accessible/workspace-tree.component.js
@@ -60,7 +60,7 @@ blocklyApp.WorkspaceTreeComponent = ng.core
                   [attr.aria-level]="level + 2">
                 <button [id]="idMap[fieldButtonInfo.baseIdKey + 'Button' + i]"
                         (click)="fieldButtonInfo.action(inputBlock.connection)"
-                        [disabled]="fieldButtonInfo.isDisabled(inputBlock.connection)">
+                        [disabled]="fieldButtonInfo.isDisabled(inputBlock.connection)" tabindex="-1">
                   {{fieldButtonInfo.translationIdForText|translate}}
                 </button>
               </li>
@@ -78,7 +78,7 @@ blocklyApp.WorkspaceTreeComponent = ng.core
                 [attr.aria-labelledBy]="generateAriaLabelledByAttr(idMap[buttonInfo.baseIdKey + 'Button'], 'blockly-button', buttonInfo.isDisabled())"
                 [attr.aria-level]="level + 2">
               <button [id]="idMap[buttonInfo.baseIdKey + 'Button']" (click)="buttonInfo.action()"
-                      [disabled]="buttonInfo.isDisabled()">
+                      [disabled]="buttonInfo.isDisabled()" tabindex="-1">
                 {{buttonInfo.translationIdForText|translate}}
               </button>
             </li>
diff --git a/accessible/workspace.component.js b/accessible/workspace.component.js
index a2c940ec0..255735020 100644
--- a/accessible/workspace.component.js
+++ b/accessible/workspace.component.js
@@ -47,7 +47,7 @@ blocklyApp.WorkspaceComponent = ng.core
 
     <div *ngIf="workspace">
       <ol #tree *ngFor="#block of workspace.topBlocks_; #i = index"
-          tabIndex="0" role="tree" class="blocklyTree blocklyWorkspaceTree"
+          tabindex="0" role="tree" class="blocklyTree blocklyWorkspaceTree"
           [attr.aria-activedescendant]="getActiveDescId(tree.id)"
           [attr.aria-labelledby]="workspaceTitle.id"
           (keydown)="onKeypress($event, tree)">