Balrog’s Blobs are classes that encapsulate the logic pertaining to a type of Release. Blobs are responsible for defining their own data structure format (with a jsonschema), the response format, and making decisions about when a response should be returned. This page documents the Blobs we have in Balrog, what they’re used for, and what responses from them look like.

App Release

App Release blobs are used for Gecko Application updates - generally anything that receives updates through MAR files (eg: Firefox, Fennec, B2G, Thunderbird). Each App Release Blob contains all of the metadata for all platforms and locales of a particular release. Here is an example that shows the Firefox-43.0.2-build1 blob, with all of its platforms and locales.

Response Format

The response for App Releases is as follows:

    <update type="minor" displayVersion="43.0.2" appVersion="43.0.2" platformVersion="43.0.2" buildID="20151221130713" detailsURL="">
        <patch type="complete" URL="" hashFunction="sha512" hashValue="781478556846b719ebc906a8a9613a421e24449b4456c4ccee990e878b3be9fb0478a78821a499a4c1f1a76d75078acf3fdfa3d0be69d2f6c94e3b6340fc935b" size="80329415"/>
        <patch type="partial" URL="" hashFunction="sha512" hashValue="6edd0803e36a03117e12a36e9fc8941e8f6321071fb00c7e8489f67b332d1cbfa95d00218e5c1b61115752fc0aecde8b2535424c521d45530455a4c5d571f889" size="39520883"/>

Some responses may have only a type=”complete” patch line, but if an <update> line is included it must have at least a <patch> block whose type=”complete”.

GMP/System Addons

GMP and System Addon updates are very similar in that they both provide a list of the latest version of addons/plugins that Firefox should install. Although the payloads they point to are different, the data structure and response are exactly the same, so they share a Blob. Here is an example that shows a GMP Blob that serves OpenH264 and CDM updates.

Response Format

The response format for GMP and System Addons is as follows:

        <addon id="gmp-eme-adobe" URL="" hashFunction="sha512" hashValue="d0077885971419a5db8e8ab9f0cb2cac236be98497aa9b6f86ff3b528788fc01a755a8dd401f391f364ff6e586204a766e61afe20cf5e597ceeb92dee9ed1ebc" size="3696996" version="15"/>
        <addon id="gmp-gmpopenh264" URL="" hashFunction="sha512" hashValue="45124a776054dcfc81bfc65ad4ff85bd65113900c86f98b70917c695cd9d8924d9b0878da39d14b2af5708029bc0346be6d7d92f1d856443b3051f0d3180894d" size="341180" version="1.5.3"/>

Similar to App Release blobs, not all <addon> lines are required, but if an <addons> block is present, at least one <addon> must be inside of it. There is no limit to the number of <addon> blocks that can be in a response, but each one must have a unique “id”.


Superblobs are used to serve multiple updates for GMP and System Addons releases. They point at the releases that should be severed for the respective query.

Superblob Example

  "products": [
  "name": "GMP-Superblob",
  "schema_version": 4000