Firefox says your storage is full (but your phone/computer isn’t): why it happens and how to fix it

If Firefox tells you storage is full (or a site shows “Quota exceeded”, “Local storage full”, or uploads won’t finish) while your device clearly has free space, the browser isn’t talking about your phone’s storage. It’s usually talking about a per-site storage limit, blocked cookies/site data, or corrupted site storage.

It’s a confusing mismatch, but it’s fixable without wiping everything.

The core idea: websites get their own “sandbox” storage inside Firefox (cookies, cache, IndexedDB, localStorage). That storage can hit limits, get blocked by privacy settings, or get stuck in a bad state.

Use the path that matches where you’re seeing it: iPhone/Android first, then Web/Desktop.

1. Why Firefox can show “storage full” when your device has space

These are the common causes behind the message (and why it can happen “suddenly”):

• Per-site quota limits: many sites store offline data in IndexedDB. Browsers cap it per site/origin, and some apps (email, docs, chat, dashboards) can hit it over time.
• Cookies/site data blocked: strict tracking protection, “block all cookies”, or certain content blockers can prevent storage writes. Some sites report that as “storage full” or “can’t save”.
• Corrupted site storage: an interrupted update, crash, or partial clear can leave a site’s storage database inconsistent, so new writes fail.
• Private browsing limitations: some storage is reduced or cleared aggressively, so apps that rely on offline storage may fail.
• Low free space threshold on mobile: even if you have space, iOS/Android can restrict app storage growth when you’re near low-storage thresholds, and the browser may surface it as a site storage error.

Knowing which one you’re hitting matters, because “clear cache” isn’t always the right first move.

Focus first on the specific site that’s failing. Don’t nuke all cookies unless you’re ready to sign back into everything.

2. Path A — iPhone/Android: fix it with the least sign-out risk

Start here if the problem shows up in Firefox on your phone.

• Step 1: Confirm you’re not in Private Browsing. If you are, open the same site in a normal tab and retry the action (saving, uploading, loading the app).
• Step 2: Free a small buffer of device space. If your phone is under roughly 1–2 GB free, create breathing room (delete a large video, offload an app, move photos). This isn’t “the” cause most of the time, but it removes one common mobile limiter.
• Step 3: Clear storage for the one site (not everything). In Firefox, remove site data/history for just that domain if the option is available. Then close and reopen Firefox and sign back into that site.
• Step 4: Temporarily relax site privacy blocking for a test. If you use Enhanced Tracking Protection on “Strict” or block all cookies, switch to “Standard” briefly or add an exception for that site. Retry the action. If it works, you’ve confirmed blocked storage/cookies was the trigger.
• Step 5: Disable extensions/content blockers (Android) for a single test. Some blockers break storage APIs indirectly. Turn them off, test, then re-enable one by one.
• Step 6: Update Firefox. Storage bugs do get patched. After updating, fully quit and relaunch the app.

If the message disappears after clearing the site’s data, it strongly points to corrupted site storage or a quota buildup for that specific site.

3. Path B — Web/Desktop (Windows/macOS/Linux): reset the site’s storage without wiping your whole profile

On desktop, you can usually fix this precisely and keep most sessions intact.

• Step 1: Test in a Private Window. If it works there, your main profile’s site storage or an extension is the likely cause (not the site itself).
• Step 2: Try with extensions disabled for one minute. Use Troubleshoot Mode (or manually disable extensions). If the issue disappears, re-enable extensions one at a time until you find the culprit.
• Step 3: Clear data for the affected site only. Go to Firefox settings for privacy/site data and remove stored data for that domain. This is the most direct fix for quota/corruption, but it can sign you out of that site.
• Step 4: Check cookie settings for that site. If you block all cookies or use strict anti-tracking settings, add an exception for the site (especially for web apps that store drafts/offline state).
• Step 5: Restart Firefox (fully) after changes. Close all Firefox windows, wait a few seconds, then reopen. Some storage databases don’t reinitialize cleanly until a full restart.

If clearing site data fixes it but it returns quickly, the site may be caching unusually large offline data (attachments, large drafts, or heavy app state). In that case, look in the site/app settings for an “offline storage” toggle or “clear cache” option inside the site itself.

4. If it still happens: quick checks that explain the stubborn cases

• Try another network (or disable VPN/proxy briefly): some networks inject filtering that breaks storage calls or service workers, and the site misreports the failure.
• Check if only one site is affected: one-site-only usually means quota/corruption. Many-sites-at-once points to cookie/storage blocking, a privacy setting, or an extension.
• Look for “clear on exit” settings: if Firefox is set to clear cookies/site data on exit, some apps behave unpredictably and can throw storage errors after relaunch.
• As a last resort, refresh/reset Firefox profile (desktop): this is bigger than clearing a site, but can resolve persistent storage database issues. Expect sign-outs and some settings loss.

Stop-point: if this only happens on one specific site across multiple browsers/devices, it’s likely a site-side quota/bug. Contact that site’s support and mention “browser storage quota / IndexedDB write failing” and the exact error text.

Final thoughts

“Storage full” in Firefox usually means “site storage can’t be written,” not “your device is out of space.” Clearing the problem site’s data (and checking cookie/privacy blocking) solves most cases without a full browser reset.

If you want the safest approach: test Private mode first, then clear data for just the affected site.