diff --git a/pxtblocks/loader.ts b/pxtblocks/loader.ts
index 7104f37deb7..495abc70d1b 100644
--- a/pxtblocks/loader.ts
+++ b/pxtblocks/loader.ts
@@ -24,6 +24,7 @@ import { initContextMenu } from "./contextMenu";
 import { renderCodeCard } from "./codecardRenderer";
 import { FieldDropdown } from "./fields/field_dropdown";
 import { setDraggableShadowBlocks, setDuplicateOnDragStrategy } from "./plugins/duplicateOnDrag";
+import { applyPolyfills } from "./polyfills";
 
 
 interface BlockDefinition {
@@ -587,6 +588,8 @@ function init(blockInfo: pxtc.BlocksInfo) {
     if (blocklyInitialized) return;
     blocklyInitialized = true;
 
+    applyPolyfills();
+
     initFieldEditors();
     initContextMenu();
     initOnStart();
diff --git a/pxtblocks/polyfills.ts b/pxtblocks/polyfills.ts
new file mode 100644
index 00000000000..dfdbd92928d
--- /dev/null
+++ b/pxtblocks/polyfills.ts
@@ -0,0 +1,60 @@
+// all options default to true
+interface CheckVisibilityOptions {
+    contentVisibilityAuto?: boolean;
+    opacityProperty?: boolean;
+    visibilityProperty?: boolean;
+    checkOpacity?: boolean;
+    checkVisibilityCSS?: boolean;
+}
+
+export function applyPolyfills() {
+    if (!(Element.prototype as any).checkVisibility) {
+        (Element.prototype as any).checkVisibility = function checkVisibility(this: Element, options: CheckVisibilityOptions = {}): boolean {
+            let checkOpacity = true;
+
+            if (options.opacityProperty != undefined || options.checkOpacity != undefined) {
+                checkOpacity = !!(options.opacityProperty || options.checkOpacity);
+            }
+
+            let checkVisibility = true;
+
+            if (options.visibilityProperty != undefined || options.checkVisibilityCSS != undefined) {
+                checkVisibility = !!(options.visibilityProperty || options.checkVisibilityCSS);
+            }
+
+            let checkContentVisibility = true;
+
+            if (options.contentVisibilityAuto != undefined) {
+                checkContentVisibility = !!options.contentVisibilityAuto;
+            }
+
+            const computedStyle = getComputedStyle(this);
+
+            // technically, this should also check for contentVisibility === "auto" and then
+            // traverse the ancestors of this node to see if any have contentVisibility set
+            // to "hidden", but Blockly doesn't use content-visibility AFAIK
+            if (
+                computedStyle.display === "none" ||
+                (checkOpacity && computedStyle.opacity === "0") ||
+                (checkVisibility && computedStyle.visibility === "hidden") ||
+                (checkContentVisibility && (computedStyle as any).contentVisibility === "hidden")
+            ) {
+                return false;
+            }
+
+            try {
+                const rec = this.getBoundingClientRect();
+                if (rec.width === 0 || rec.height === 0) {
+                    return false;
+                }
+            }
+            catch {
+                // some versions of firefox throw if an element is not in the DOM
+                // and getBoundingClientRect is called
+                return false;
+            }
+
+            return true;
+        }
+    }
+}
\ No newline at end of file