Real-world examples of memory leaks in web browser extensions: 3 examples that keep happening in 2025

1. Long‑lived background scripts holding onto tab data

When developers talk about examples of memory leaks in web browser extensions, background scripts are usually at the top of the list. Modern browsers like Chrome and Edge use a service worker–style background process for Manifest V3, but many older or still‑supported extensions rely on long‑lived background pages. Those background contexts are perfect leak factories.

Here’s a classic example of how it happens:

• An extension listens for chrome.tabs.onUpdated and chrome.tabs.onRemoved.
• Every time a tab loads, the extension stores metadata in a global tabsCache object.
• When a tab closes, the extension forgets to remove the entry from tabsCache.

The result: after opening and closing hundreds of tabs during a normal workday, the background page still holds references to every tab’s data. Even though the tabs themselves are gone, the JavaScript objects live on, keeping memory allocated.

In practice, this pattern shows up in several real examples:

• A tab manager that tracks tab history but never prunes closed tabs.
• A session saver that only adds new entries and never expires old ones.
• A research helper extension that caches page titles and snippets forever.

You can see the impact using Chrome’s built‑in Task Manager (Shift+Esc on Windows). A healthy extension hovers at a steady memory footprint; a leaky background script will slowly climb over hours of use.

From a debugging perspective, the browser DevTools Memory panel is your friend. Take two heap snapshots: one after opening many tabs, and one after closing them. If the background context still holds large arrays or maps keyed by tab ID, you’ve found one of the most common examples of memory leaks in web browser extensions.

2. Content scripts that never clean up DOM references

Another category of examples of memory leaks in web browser extensions: content scripts that attach themselves to pages and then forget to leave.

A typical scenario looks like this:

• The extension injects a content script into every matching page.
• The script queries the DOM (document.querySelectorAll) and stores references to many nodes.
• It attaches event listeners to elements or to window / document.
• When the user navigates or the tab is re-used (think single‑page apps), the script does not remove listeners or clear references.

Modern web apps like Gmail, YouTube, Slack, and many React/SPA sites reuse the same page shell and swap content dynamically. If your content script assumes a full page reload, you get creeping leaks:

• A price tracker extension that injects tooltips into product listings on Amazon and keeps arrays of DOM nodes around for later use.
• A grammar checker that tracks every editable field on the page but never unregisters mutation observers when the user navigates within the SPA.
• A note‑taking extension that overlays icons next to links and keeps a global allLinkIcons array that is never emptied.

Each navigation adds more listeners and more DOM references. The browser’s garbage collector can’t reclaim those nodes because the extension still holds pointers to them.

To see this in action, open Chrome DevTools on a page with an active extension content script, then:

• Watch the Performance and Memory panels while navigating inside a SPA.
• Use Performance recordings to capture timeline allocations.
• Take repeated heap snapshots; if detached DOM trees keep growing, you’ve hit another one of those best examples of extension memory leaks.

Mozilla’s documentation on extension memory behavior is a good reference for how content scripts interact with page lifecycles: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Content_scripts

3. Message listeners and ports that never close

The third big pattern in our examples of memory leaks in web browser extensions: 3 examples set revolves around messaging. Extensions rely heavily on runtime.sendMessage, tabs.sendMessage, and long‑lived runtime.connect ports to coordinate between background scripts, popups, and content scripts.

Here’s how leaks creep in:

• A popup opens and calls chrome.runtime.connect to the background.
• The background script stores the port object in an array or map.
• When the popup closes, the code forgets to remove the corresponding port from that data structure.

Multiply that by every popup open/close cycle, and the background script slowly accumulates dead ports and associated state. In more complex extensions, each port might carry a user session object, cached API data, or timers.

Some real examples include:

• A chat helper extension that opens a port for each conversation window and keeps a history buffer attached to the port object.
• A stock‑tracking extension where every popup opens a streaming connection to a backend via the background script; the port is never fully cleaned up.
• A password manager popup that keeps encrypted vault data in memory as long as the port exists, but doesn’t clear it when the popup disappears.

These are subtle examples of memory leaks in web browser extensions because everything appears to “work.” The user closes the popup, sees it disappear, and assumes the resources went with it.

The fix usually involves:

• Listening for port.onDisconnect and removing all references to the port.
• Clearing any intervals, timeouts, or observers tied to that port.
• Avoiding global arrays of ports unless you rigorously prune them.

Google’s Chrome Extensions documentation on messaging offers patterns for correctly managing ports: https://developer.chrome.com/docs/extensions/develop/messaging

Beyond the big three: more real examples of extension memory leaks

The three categories above are the headline examples of memory leaks in web browser extensions, but they’re not the whole story. In 2024–2025, as extensions get more complex and more integrated with cloud services, several other patterns keep showing up in bug reports and performance complaints.

Leaky timers and intervals in background or popup scripts

Extensions love timers:

• Polling remote APIs for updates.
• Periodically scanning tabs or the DOM.
• Updating UI badges every few seconds.

A very common example of a leak:

• A popup script starts a setInterval when opened.
• The popup closes, but the interval isn’t cleared in all code paths.
• The browser keeps the context alive longer than expected, or the background script accumulates timer callbacks tied to stale state.

Over time, you get a growing pile of active timers, each holding references to data and sometimes to DOM nodes (in the popup case). This is especially visible in extensions that show live CPU, memory, or stock price graphs.

Caches that grow without limits

Another class of best examples of bad memory behavior: unbounded caches. Developers often cache:

• API responses per domain.
• Parsed JSON data from user history.
• Image or icon data for quick rendering.

If there is no eviction strategy, the cache just grows. A browser session that stays open for days or weeks becomes a long‑running process with ever‑increasing memory.

Real‑world style examples include:

• A shopping assistant that caches product details and images for every product viewed across dozens of sites, never expiring old entries.
• A translation extension that stores every translated sentence in memory for “instant recall,” but never prunes the dictionary.
• A developer tool extension that logs network requests for debugging and keeps all logs in memory until the browser restarts.

In many cases, developers assume that extensions are short‑lived. In reality, some users keep a single browser session running for weeks on laptops and desktops. That turns a mild cache into a long‑term leak.

Detached DOM trees from UI overlays

Extensions that draw overlays—tooltips, sidebars, floating widgets—can easily create detached DOM trees:

• The extension injects an overlay element.
• The user closes or hides the overlay.
• The extension removes the element from the DOM, but still keeps references in JavaScript.

From the garbage collector’s perspective, those DOM nodes are still reachable, so they stay in memory. Over time, repeated open/close cycles build up a graveyard of detached DOM trees.

This pattern is frequently seen in:

• Screenshot extensions that draw selection rectangles.
• Note‑taking or annotation tools that add highlights and comments.
• Reading‑mode extensions that rewrite the DOM and keep old versions in memory for “undo” features.

The MDN Web Docs have a good high‑level explanation of how detached DOM trees contribute to leaks in JavaScript contexts: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Memory_management

2024–2025 trends: why leaks in extensions matter more now

Two trends make these examples of memory leaks in web browser extensions more painful than they were a few years ago:

1. Heavier web apps and more tabs
   Users routinely keep 20–100 tabs open, many running heavy apps like Figma, Notion, or cloud IDEs. Add a few leaky extensions on top, and you hit swap territory fast, especially on 8 GB machines.

2. Manifest V3 and service workers
   Manifest V3 pushes extensions toward service worker–based backgrounds that spin up and down. This helps with some leaks, but it also introduces new patterns where developers store large state in chrome.storage or in global variables that get rehydrated on every wake‑up. Poorly designed, this can cause repeated allocations and fragmentation.

Performance complaints in extension reviews have become more common. Users may not say “memory leak,” but they definitely say “Chrome is slow now” or “my laptop fans go crazy when I install this.” In other words, these real examples of extension memory leaks have direct product and reputation impact.

How to spot these examples of memory leaks in your own extension

If you’re building or maintaining an extension, you can use the patterns above as a checklist rather than waiting for angry reviews.

Key practices:

• Monitor extension processes using the browser’s task manager. Watch memory over time while performing typical user flows.
• Use heap snapshots in DevTools to look for:
  • Detached DOM trees.
  • Growing arrays or maps keyed by tab IDs, ports, or URLs.
  • Objects that should be short‑lived but accumulate across snapshots.
• Stress‑test navigation on SPA‑heavy sites (Gmail, YouTube, large React apps) to see if your content scripts leak.
• Simulate long sessions by keeping the browser open for hours or days in a test environment and watching whether your extension’s memory stabilizes.

While there isn’t a single “official” memory‑leak test harness for extensions, the general browser performance tooling described in resources from organizations like the W3C and MDN apply directly to extension contexts.

FAQ: common questions about memory leaks in extensions

What are some common examples of memory leaks in web browser extensions?

Common examples include:

• Background pages that keep tab data in global objects and never remove it when tabs close.
• Content scripts that attach event listeners and keep DOM references across SPA navigations.
• Long‑lived message ports that are never removed from internal arrays or maps.
• Popup scripts that start timers and intervals without clearing them when the popup closes.
• Caches that grow indefinitely with API responses, images, or logs.

These examples of memory leaks in web browser extensions all follow the same pattern: something that should be temporary ends up referenced forever.

Can a single extension memory leak slow down my entire browser?

Yes. If one extension steadily increases its memory usage, it competes with tabs and other extensions for RAM. On systems with limited memory, the OS starts swapping to disk, which makes everything feel slow. Users often blame the browser, but a few leaky extensions are enough to cause the problem.

How do I test for an example of a memory leak in my own extension?

A simple approach:

• Install your extension in a fresh browser profile.
• Open DevTools for the background page or service worker.
• Perform a set of actions repeatedly: open/close popups, navigate between pages, open/close tabs.
• Take multiple heap snapshots during the process.

If memory usage continually grows and snapshots show accumulating objects or detached DOM trees, you’ve found a real example of a memory leak.

Are Manifest V3 extensions safe from these examples of leaks?

No. Manifest V3 reduces some classes of leaks by using service workers that can be suspended, but it doesn’t magically eliminate all the examples of memory leaks in web browser extensions. You can still:

• Hold onto large data structures in global scope.
• Recreate big caches on every wake‑up without clearing them.
• Leak through content scripts, overlays, and messaging.

Good lifecycle management and disciplined cleanup are still required.

The bottom line: the best examples of memory leaks in web browser extensions tend to repeat the same mistakes—unbounded caches, forgotten listeners, and long‑lived references to things that should have been temporary. If you learn to recognize those patterns, you can keep your own extensions from turning into silent RAM hoarders.