Enabling WebExtensions storage.local IndexedDB backend by default on Nightly

Luca Greco lgreco at mozilla.com
Fri Aug 3 18:22:30 UTC 2018

As many already know, we have been working on a new backend for the
storage.local WebExtensions API based on IndexedDB.

Before enabling it by default on Nightly, we have tracked down and fixed
all the potential issues that we have been able to identify while the new
backend was disabled by default. We have been keeping track of the progress
on Bug 1474562 - Enable ExtensionStorageIDB backend on Nightly

Now it is time to test the new backend for real. Once the patch lands in
Nightly (which should be very soon) and your Nightly build updates, all the
extensions enabled in the related Firefox profile will start migrating to
the new backend.

The new backend is going to reduce the performance impact of the
storage.local API on Firefox itself [1], but it’s a completely new backend
and so:


   it has to migrate the existing data from the JSONFile currently used
   into an IndexedDB database (and there is no automatic migration back to the


   it may still have some behaviors that differ from the current backend in
   subtle ways and affect only some extensions and/or some users

We need your help to track down any further issues with the new backend
once it has been enabled by default.

Please report any issue that seems to be related to the storage.local API
on Bugzilla

Please add it as a blocker of Bug 1474562
<https://bugzilla.mozilla.org/show_bug.cgi?id=1474562> so that we can
promptly investigate it and work on fixing it.

If any of the extensions that you have installed seem to have lost their
data, or seem to be misbehaving, don’t panic. The data migration in Nightly
does not remove the old data file (it has been renamed), and you can find
more information about how to retrieve and re-import the extension data in
the following post on the Add-ons Blog

Developers, if you receive complaints from users who may be affected by
this migration, please refer them to the blog post.



[1]: e.g. you may watch the screencast linked to
https://bugzilla.mozilla.org/show_bug.cgi?id=1477015#c18 to get an idea of
the performance impact of the current JSONFile backend compared to the
IndexedDB backend.
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