Why uBlock Origin requests to store unlimited data in Firefox

Martin Brinkmann
Mar 27, 2019
Updated • Mar 27, 2019

Firefox users who have the content blocker uBlock Origin installed receive a permission prompt currently when uBlock Origin is updating.

The prompt requests permission to store unlimited amounts of data. Firefox displays the prompt during the upgrade of uBlock Origin. The two options that are provided are to allow the permission by selecting "update" or to disallow it by selecting cancel.

ublock origin permissions

The prompt reads:

uBlock Origin has been updated. You must approve new permissions before the updated version will install.

Choosing "cancel" will maintain your current add-on version.

It requires your permission to:

Store unlimited amount of client-side data.

The update won't be installed if you select cancel. The change brings the uBlock Origin extension for Firefox in line with the Chrome extension. Chromium-based versions of uBlock Origin requested the permission since 2014 when the extension was first published.

Mozilla notes that extensions should only request the unlimited storage permission of they use more than 5 Megabytes of storage; this is the case for uBlock Origin as it uses more than 5 Megabytes of local storage in its default configuration.

The change has no impact on the functionality of the extension at this point. Firefox does not enforce local storage quotas which means that extensions may store more than 5 Megabytes of storage even if they don't request the permission currently.

It is possible that the storage limit will be enforced eventually, however. The new permission request in uBlock Origin is a preemptive one to avoid issues in the future if the limit is enforced by Mozilla.

While preemptive in nature, it is still justified as the extension uses more than 5 Megabytes of local storage in its base configuration.

Closing Words

The permission brings uBlock Origin in line with the Chrome version of the extension. Firefox users who want to continue using up to date versions of the browser extension need to allow the new permission by selecting update.

Now You: Do you use a content blocker in your browser of choice?

Why uBlock Origin requests to store unlimited data in Firefox
Article Name
Why uBlock Origin requests to store unlimited data in Firefox
Firefox users who have the content blocker uBlock Origin installed receive a permission prompt currently when uBlock Origin is updating.
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  1. Hugh Jarce said on October 11, 2020 at 12:13 pm

    People, stop writing “uBlock” when you mean “uBlock Origin”, they’re two different products.

  2. LC said on April 23, 2019 at 6:02 pm

    My comment goes directly to ublock: Come on guys, unlimited???, let’s be reasonable…

  3. Dave said on April 3, 2019 at 11:54 pm

    This new Permission has killed other extensions ie CONTEXT SEARCH
    and have proved it by reinstalling a backup I made a week ago
    it is only when I grant it that it kills context search.

    Time to find a new ad blocker

  4. Anonymous said on March 29, 2019 at 8:56 pm

    uBlock Origin and pretty much every adblocker had the ‘unlimited storage’ feature from day 1.

  5. Nurvien Alarick said on March 29, 2019 at 5:12 pm

    Genious, lets have unlimited data storage, then someone can hack, abuse it and do whatever they want, just another attack vector.

    What would be smart is fixed storage that suits ublock and its lists and if needs more just prompt user.

    But who cares about any of that, lets do the opposite of logic.

  6. 4t4v1c said on March 28, 2019 at 10:18 pm

    You can see the filterlists and you can see when they are updated and you can prevent the update.

    uBo does not transmit its stored data!

    “uBlock Origin does not have a dedicated server, it can’t “phone home” with your browsing data”.

    See: https://github.com/gorhill/uBlock/wiki/

  7. D said on March 28, 2019 at 3:38 pm

    Can we view all the data stored by uBlock? Does the program ever trasmit the data it stores?

    1. Anonymous said on March 29, 2019 at 9:00 pm

      You can view all the filter lists that you currently have, yes/
      uBO does not have a dedicated server.

  8. 11r20 said on March 28, 2019 at 2:37 am

    I have never noticed any ‘uB’ download in the temp file larger than 3MB’s…I also check
    the block lists manually as they are updating
    and all temp file’s are purged on shutdown

    I update manually and do not use the cloud
    storage…I see exactly what certain IP’s
    are used when updating by watching my netlimiter program…everything works as it should on uBlock original 1.13.8

    Pi-hole works great for me as well…That bein said I like the clean late 80’s IBM look of my personal server/computer on an old 27 inch screen

    Thanks fer the heads-up Mr. Martin ‘Sir’

  9. Tuncay said on March 28, 2019 at 2:36 am

    And one more thing what does this commits mean?


    Can developers explain us?

    1. uBlock-user said on March 28, 2019 at 7:49 am

      gorhill — “The Chromium version of uBO has declared `unlimitedStorage` since the
      extension was first published in 2014. Declaring this permission in
      Firefox brings uBO inline with the Chromium version. I suspect some
      reported errors could be caused by IndexedDB eviction due to the lack
      of `unlimitedStorage` permission.”

  10. Tuncay said on March 28, 2019 at 2:33 am

    I am using uBlock in everywhere but i cancelled. Should i update and approve that permission? I am really confused because i don’t know what does it mean by store unlimited data.

    1. Martin Brinkmann said on March 28, 2019 at 5:49 am

      Yes you should update, the term “unlimited” makes it sound as if uBlock would suddenly use much more space on the disk but that is not the case.

  11. Mike W. said on March 28, 2019 at 12:56 am

    I use uBlock Origin everywhere I can. Only places I don’t is on my Android phone (Samsung Internet Beta w/AdGuard) and Brave (Brave Shields are basically uBlock w/o cosmetic filtering). I can’t imagine browsing the web without uBlock.

  12. Dennis said on March 27, 2019 at 10:57 pm

    I got that notification and forgotten all about it until our gracious host brought this to my attention. I just clicked “Update” without even really reading it, or even giving it a second thought!

    Seemed legit……. I really like and trust UBO……

    I hadn’t realised this is the way it has always worked with Chromium. It’s always good to know these things.

    Thanks, Martin!

  13. Anonymous said on March 27, 2019 at 10:52 pm

    Filter lists! EasyList alone is nearly 3 megabytes.

  14. DrKnow said on March 27, 2019 at 9:23 pm

    Do they also phone home when you turn off auto update?

  15. Jael said on March 27, 2019 at 8:09 pm

    I’m confused as to what uBlock is storing in the first place. I’ve tried looking it up in various ways but nothing comes up explaining it. If all it’s supposed to do is block ads why does it need “unlimited client side data” storage space?

    1. Anonymous said on March 27, 2019 at 11:37 pm

      Ad-blockers are storing lists of elements they should block.

    2. Croatoan said on March 27, 2019 at 11:34 pm

      It uses lists so it can block ads. Lists are really large.

      1. squirtle said on April 22, 2019 at 4:08 am

        “It stores lists” does not seem like a valid response- if the list is a document, text data uses very little space. It should take a very long list to approach 5mb. What’s the biggest text file on your computer?

      2. gwarser said on April 22, 2019 at 10:57 am

        EasyList alone is nearly 3 megabytes. uBlock Origin also keeps snapshot of “compiled” (internal representation) to load them faster on startup.

      3. sam said on March 30, 2019 at 1:20 pm

        It reads: “In a future version, uBO may start to use a “persistent” indexedDB instance for its cache storage to ensure proper functioning of uBO.[1] uBO currently uses a non-persistent indexedDB instance and this may cause difficult to diagnose issues for some users as Firefox may evict uBO’s cache storage at any time.”

        I worry this cache storage could be hacked and used to get indirectly our browsing history or preferences without for us the possibility to void this cache.

        This indexedDB is supposed to list the adds, which might content pieces of information crucial to understand someone’s habits and preferences.

      4. uncommon sense said on May 29, 2019 at 3:06 pm

        @sam indexedDB is per-site and per-addon. You can’t do cross-database lookups. It does not contain any browsing history.

        if you’re worried about indexedDB and all it does is store cached stuff, look in C:\Windows\Temp or your AppData folder…

      5. Jael said on March 28, 2019 at 2:49 am

        Holy. I feel so dumb now. I blame the fact that I’ve been studying non-stop for 10+ hours a day every day for the past week. Like how tf did I forget that it uses lists? I’m dumb LOL


  16. dedup said on March 27, 2019 at 7:29 pm

    i’ve downloaded filters lists for ublock and I realised that all of them phone home (for update) when firefox starts. It seems that most of them are hosted by Amazon services (AWS ?) Google etc.

  17. Anonymous said on March 27, 2019 at 5:40 pm

    Thank you for the information, very fast!

  18. TelV said on March 27, 2019 at 3:47 pm

    I stick with ABP+ v2.9.1 and the Element Hiding Helper v1.4 on Waterfox. Those two together with Decentraleyes, Privacy Badger and various other anti-tracking add-ons.

    I’ve switched to using Cloudflare DNS now since my VPN’s DNS servers are located in Sweden which causes problems with online shopping since everything gets priced in SEK instead of euro.

    1. Cloudnoflare said on March 28, 2019 at 10:13 pm

      @TelV But Dude, Cl0udfl4r3 is tracking you.

  19. Ray said on March 27, 2019 at 1:37 pm

    The web of 2019 is borderline, nay, completely unusable without a content blocker. uBlock Origin is my drug of choice for this at work or on my phone, otherwise a DNS filter at home through a piHole.

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