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firefox-devtools-mcp

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set_download_behavior

Control download handling by saving files to a specified folder, canceling them, or restoring default behavior without the native file dialog.

Instructions

Control how downloads are handled: allow (save to a destination folder), deny (cancel), or reset to default. Avoids the native save-file dialog. Requires a recent Firefox.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
behaviorYes'allowed' saves downloads to `downloadFolder`, 'denied' cancels them, 'default' resets to the browser default
downloadFolderNoPath to the folder where downloads should be stored, created if missing. Only used for behavior='allowed', where it defaults to ~/.firefox-devtools-mcp/output/downloads. Relative paths resolve against the current working directory.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changedv0.10.3
    • changedInput schema / properties / behavior / description
      Previous value: -"'allowed' saves downloads automatically, 'denied' cancels them, 'default' resets to the browser default"New value: +"'allowed' saves downloads to `downloadFolder`, 'denied' cancels them, 'default' resets to the browser default"
    • addedInput schema / properties / downloadFolder
      Added value: +{
+  "description": "Path to the folder where downloads should be stored, created if missing. Only used for behavior='allowed', where it defaults to ~/.firefox-devtools-mcp/output/downloads. Relative paths resolve against the current working directory.",
+  "type": "string"
+}
  2. Addedv0.9.15

TDQS

A4/5.0
Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries the full burden. It discloses key behaviors: that it avoids the save-file dialog and requires a recent Firefox. It also hints at side effects (e.g., changing download handling policy). However, it doesn't detail what happens on success/failure, persistence of changes, or impact on in-progress downloads, leaving some behavioral ambiguity.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is two sentences with no waste. The main action ('Control how downloads are handled') is front-loaded, followed by the option list, a key benefit, and a requirement. Every element earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple two-parameter setter with a fully descriptive schema and no output schema, the description adequately covers what an agent needs to call it correctly. It includes a prerequisite and the primary purpose. Minor omissions like persistent side effects or error behavior are not critical given the tool's simplicity, so it is nearly complete.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the schema already documents both parameters (behavior enum and downloadFolder default/path resolution). The description's mention of 'allow (save to a destination folder)' and 'deny (cancel)' only paraphrases the schema's behavior description without adding new meaning or usage nuance, so it meets the baseline but adds little beyond the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's purpose with a specific verb ('Control') and resource ('downloads'), and enumerates the three distinct behaviors (allow, deny, reset). It also adds a unique behavioral note ('Avoids the native save-file dialog') that distinguishes it from download-related siblings like list_downloads or clear_downloads.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides clear context for use, including the benefit of avoiding the native save-file dialog and a prerequisite ('Requires a recent Firefox'). However, it does not explicitly contrast with sibling tools (e.g., when to use list_downloads instead) or state exclusion scenarios, so it stops short of full guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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