Over recent months, many web developers and users began noticing a frustrating error while trying to use Firefox: an unexpected NS_ERROR_DOM_QUOTA_REACHED when web applications attempted to save data to localStorage or IndexedDB. The issue seemed perplexing—particularly on sites that had worked flawlessly before. This seemingly obscure error message pointed to a bigger and often misunderstood problem regarding browser storage quotas and how Firefox manages persistent data. But what caused the problem? Why now? And how was it fixed?

TL;DR

Firefox users and developers encountered NS_ERROR_DOM_QUOTA_REACHED due to uncollected storage data building up in the background, breaching internal browser quotas. Changes in Firefox’s internal policies and evolving storage usage patterns led to aggressive storage limits triggering more often. The solution came in the form of an IndexedDB quota cleanup mechanism introduced by Firefox to automatically remove outdated or unused data, restoring storage availability for modern web apps. This update has significantly improved the resilience and predictability of browser-based storage.

What led to the Quota Reached problem?

The error message NS_ERROR_DOM_QUOTA_REACHED is thrown by Firefox when a web app attempts to exceed the allowed limit for client-side storage mechanisms like localStorage, sessionStorage, or IndexedDB. For most users, these limits tend to go unnoticed because average pages don’t usually push the boundaries of storage. However, modern applications—offline-first web apps, collaborative tools like Notion or Figma, and data-heavy dashboards—routinely store megabytes of structured data locally for faster user experiences.

With Firefox prioritizing privacy and user control, the browser caps storage in ways that aren’t simply proportional to disk space. Internal policies consider:

• Total disk usage by Firefox
• Storage consumption by individual domains
• Time since last visit to a site
• Whether the storage has been marked as persistent

As websites grew more complex and started to make heavier use of client-side databases, more began running into these limits. A critical characteristic was that Firefox would not automatically purge unused data, even if it was no longer needed by the application or hadn’t been used in months or years. This resulted in bloated storage profiles that choked new data from being saved—hence, the sudden explosion of the quota reached errors.

[h2>Tracking Down the Source

Professional developers trying to debug the quota issue often found that the problem wasn’t immediately clear. Clearing cache didn’t fix it. Neither did restarting the browser. Using incognito mode worked—because it didn’t carry over years of accumulated IndexedDB objects—but that wasn’t a viable long-term solution.

In fact, it turned out that not the new data but the old, unused data was blocking everything. Data stored in previous versions of apps or by third-party libraries lingered in IndexedDB, never being cleaned up. One common example was calendar or note-taking apps storing every calendar invite since 2015—data the app no longer accessed, but which still counted toward the quota.

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How Quotas Are Calculated

While developers often assume there’s a fixed quota amount per domain, that’s not entirely accurate with Firefox. The quota system is more dynamic:

• It typically starts with 50% of available disk space allocated to Firefox storage
• Each origin (i.e., website domain) gets a fraction of that, determined by usage patterns and user behavior
• Origins that are visited more frequently or get marked as “persistent” have slightly higher limits

This model strives for fairness, but in practice it meant that a user could hoard storage across dozens of barely-active sites until the entire browser crossed its quota envelope. The error then started appearing, not just on the bloated sites, but anywhere trying to add data—especially if the origin had no persistent storage flag.

The IndexedDB Quota Cleanup Fix

Recognizing the seriousness of the issue—especially for modern, feature-rich web apps—Mozilla introduced a fix that landed as part of an update in early 2024. This fix focused on IndexedDB quota cleanup—a background process in Firefox that periodically identifies stale or abandoned data stores and purges them to free up space.

Key aspects of this fix included:

• Age-based cleanup: Databases not accessed in several months act as candidates for removal
• Size thresholds: Domains using disproportionate amounts of storage get trimmed
• Privacy integration: Data from trackers or third-party cookies faces stricter retention rules

[p ai-img]indexeddb cleanup, firefox, storage management[/ai-img]

The feature works in the background and is cautious—only removing data unlikely to be used by active sessions. It also adds monitoring for extensions and system settings that might prevent cleanup from occurring. This update marked the beginning of a more dynamic approach in Firefox to balancing rich web application needs with responsible resource usage.

Developer Best Practices Going Forward

Web developers can take certain precautions to avoid running headfirst into this problem again:

• Implement logic to clear outdated entries in IndexedDB periodically
• Use navigator.storage.persist() to request persistent storage where appropriate
• Gracefully handle quota exceptions with user-facing messages and rollback possibilities
• Regularly audit what’s stored locally, especially when migrating app versions

With these strategies, web apps can minimize storage waste and remain resilient even as browser internals evolve.

Conclusion

The NS_ERROR_DOM_QUOTA_REACHED error in Firefox was more than just a technical hiccup. It was a signal pointing toward browser resource constraints becoming a real-world issue in the age of heavy web applications. Thanks to the IndexedDB quota cleanup project, Mozilla has helped reinstate trust in the robustness of modern web storage. Users benefit from fewer unexpected errors, and developers can look forward to more consistent behavior across sessions.

FAQ – IndexedDB Errors and Fixes in Firefox

• Q: What is NS_ERROR_DOM_QUOTA_REACHED?
  A: It’s a Firefox error that means the maximum allowed local storage has been used up for a website. It usually occurs when trying to write to IndexedDB or localStorage.
• Q: Why does this only happen in Firefox and not other browsers?
  A: Each browser has different rules for calculating and enforcing storage quotas. Firefox’s approach emphasizes privacy and proactive space management, which sometimes limits more aggressively than Chromium-based browsers.
• Q: How can I fix this issue as a user?
  A: Clearing site data from Settings → Privacy & Security → Cookies and Site Data often resolves the problem. However, this may sign you out or remove offline data from some apps.
• Q: How can a developer prevent future quota issues?
  A: Use storage responsibly—regularly remove stale data, handle exceptions gracefully, and request persistent storage when necessary through the StorageManager API.
• Q: Is the issue completely fixed with Firefox’s update?
  A: The update dramatically reduces the frequency of this error by cleaning up unused data proactively. While not infallible, it should keep routine app usage well within safe storage limits.