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A Firefox add-on can begin with a small change to manifest.json: the configuration file that gives an extension its name and version and connects its code to browser features. Mozilla’s documentation provides a practical path for loading and testing a first extension, but it does not establish what this author’s add-on did or which manifest field changed. Those details belong to the author’s own story, not to Mozilla’s example.
What a manifest change can do
Mozilla describes manifest.json as the only file every extension using WebExtension APIs must contain. The manifest holds basic metadata and can also declare functionality such as background scripts, content scripts, and browser actions. In MDN’s general manifest summary, manifest_version, name, and version are the required keys. MDN’s manifest reference explains the format and available keys.
A manifest edit can also determine when and where extension code runs. For instance, MDN’s tutorial uses a content-script match pattern to connect a JavaScript file to selected web pages. That is Mozilla’s Borderify demonstration, not evidence about this add-on: the author’s purpose, changed field, and test results are not specified here.
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MDN’s first-extension walkthrough uses a project folder containing a manifest, a JavaScript file, and optionally an icon. To try an extension in Firefox without distributing it, the tutorial gives this workflow:
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- Open
about:debuggingin Firefox. - Select This Firefox.
- Choose Load Temporary Add-on.
- Select a file in the extension’s project directory.
The temporary installation remains until Firefox restarts. After changing the extension’s files, MDN’s walkthrough describes reloading the extension to test the update. See MDN’s first WebExtension walkthrough for the tutorial’s complete example.
Choose permissions for the feature
Permissions should follow the extension’s actual behavior. Host permissions specify URL patterns and can authorize capabilities such as injecting scripts or styles on matching pages. For some tasks, activeTab offers narrower access: it grants additional access to the active tab after the user interacts with the extension. These options have different scopes; the right choice depends on what the add-on needs to do. MDN documents them in its permissions reference.
Temporary testing is different from public distribution
Loading an add-on temporarily is a local development workflow, not a way to give a finished extension to other people. MDN says distribution requires packaging the extension and submitting it to Mozilla for signing. Its tutorial also includes Firefox publishing details such as browser_specific_settings.gecko.id and data_collection_permissions for its example. Those publishing particulars should not be confused with the three keys in MDN’s general summary of a basic manifest; consult Mozilla’s current documentation for requirements that apply to a real submission.
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