Mozilla cookie export format fields

Understanding Mozilla's Cookie Export Format Fields

Explore the structure and meaning of fields within Mozilla's cookie export format, crucial for developers and users managing browser data.

Mozilla Firefox, like other web browsers, stores website-specific data in 'cookies'. These small pieces of data are essential for maintaining user sessions, personalization, and tracking. When you export cookies from Firefox, they typically follow a specific format, often a tab-separated values (TSV) file, which can then be imported into other browsers or tools. Understanding the fields within this format is key to correctly interpreting and manipulating cookie data.

Standard Cookie Export Fields

The standard Mozilla cookie export format, often seen in files like cookies.txt (Netscape format), includes several distinct fields. Each line in the file represents a single cookie and its associated properties. These fields are crucial for defining the cookie's behavior, scope, and lifespan. The order and interpretation of these fields are consistent, making it possible for various tools to parse them reliably.

flowchart LR
    subgraph Cookie Fields
        A[Domain] --> B[Flag]
        B --> C[Path]
        C --> D[Secure]
        D --> E[Expiration]
        E --> F[Name]
        F --> G[Value]
    end
    G --> H{Cookie Data Line}

Flowchart illustrating the sequence of fields in a Mozilla cookie export line.

# .netscape HTTP Cookie File
# This is a generated file!  Do not edit.
.example.com	TRUE	/	FALSE	1678886400	mycookie	myvalue
.another.org	FALSE	/path	TRUE	1709424000	sessionid	abcdef123456

Example of a Mozilla-style cookies.txt file.

Detailed Field Breakdown

Let's delve into each field to understand its purpose and the type of data it holds. This detailed breakdown will help in debugging cookie-related issues or when manually constructing cookie files.

1. Domain

This field specifies the domain for which the cookie is valid. A leading dot (.) indicates that the cookie is valid for all subdomains of the specified domain (e.g., .example.com means www.example.com, sub.example.com, etc.). If there's no leading dot, the cookie is only valid for the exact domain specified.

2. Flag

Often referred to as 'Include Subdomains' or 'Domain-level cookie'. This boolean field (TRUE or FALSE) indicates whether the cookie is accessible by subdomains. In the Netscape format, TRUE typically means the cookie is valid for subdomains (matching the leading dot convention in the Domain field), while FALSE means it's only for the exact domain.

3. Path

This field defines the URL path within the domain for which the cookie is valid. For example, / means the cookie is valid for all paths on the domain, while /app/ means it's only valid for URLs starting with /app/.

4. Secure

Another boolean field (TRUE or FALSE). If TRUE, the cookie will only be sent over secure (HTTPS) connections. If FALSE, it can be sent over both HTTP and HTTPS.

5. Expiration

This field contains a Unix timestamp (number of seconds since January 1, 1970, UTC) indicating when the cookie will expire. After this time, the browser should delete the cookie. A value of 0 or a very low number often indicates a session cookie, which expires when the browser session ends.

6. Name

This is the actual name of the cookie, as set by the web server. It's a string that identifies the cookie (e.g., sessionid, user_pref).

7. Value

This is the data associated with the cookie's name. It's a string that holds the actual information the server wants to store (e.g., abcdef123456, dark_theme).

Parsing and Using Exported Cookies

When working with exported cookies, especially in scripting or development contexts, understanding how to parse these fields is essential. Many programming languages offer libraries or simple string manipulation functions to handle TSV files. The key is to split each line by the tab character and then interpret each resulting token based on its position.

Python Parsing Example

def parse_cookie_line(line): parts = line.strip().split('\t') if len(parts) == 7: return { 'domain': parts[0], 'flag': parts[1] == 'TRUE', 'path': parts[2], 'secure': parts[3] == 'TRUE', 'expiration': int(parts[4]), 'name': parts[5], 'value': parts[6] } return None

cookie_line = '.example.com\tTRUE\t/\tFALSE\t1678886400\tmycookie\tmyvalue' parsed_cookie = parse_cookie_line(cookie_line) print(parsed_cookie)

JavaScript Parsing Example

function parseCookieLine(line) { const parts = line.trim().split('\t'); if (parts.length === 7) { return { domain: parts[0], flag: parts[1] === 'TRUE', path: parts[2], secure: parts[3] === 'TRUE', expiration: parseInt(parts[4], 10), name: parts[5], value: parts[6] }; } return null; }

const cookieLine = '.example.com\tTRUE\t/\tFALSE\t1678886400\tmycookie\tmyvalue'; const parsedCookie = parseCookieLine(cookieLine); console.log(parsedCookie);