Merge changes from padenot/firefox-devtools-mcp#46
Merged
freema merged 20 commits intomozilla:mainfrom Mar 28, 2026
Merged
Conversation
- CLI: --env and --output-file flags
- Capture stdout/stderr via fd redirection
- Tools: get_firefox_output, get_firefox_info, restart_firefox
- Change Firefox config at runtime without MCP server restart:
different binary, env var, etc.
This implements: - list_chrome_context - select_chrome_context - evaluate_chrome_script They do what they say on the tin, but this requires `MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1`, as expected. This allows some functionnality for Firefox javascript developers.
Check connection status before restart to avoid errors when Firefox was closed externally. Fall back to CLI firefoxPath if not provided. Clean up stale instances and update error messages to guide recovery.
Selenium's setProfile() copies the profile to a temp directory which can silently fail or not preserve all profile data. Using Firefox's native --profile command-line argument directly ensures the configured profile is actually used. Adds test to verify profile path is passed via --profile argument.
Previously, restart_firefox would lose the configured profile path when restarting Firefox. Now the tool preserves the current profile path by default and adds a profilePath parameter to allow changing it at runtime. Documentation updated to reflect: - New profilePath parameter in restart_firefox - Firefox management tools in tool overview - Corrected profile management behavior (uses native --profile arg)
Allow overriding Firefox's RecommendedPreferences via CLI and runtime tools. When Firefox runs in WebDriver BiDi mode, it applies preferences that change default behavior for test reliability. This feature enables Firefox developers and testers to override these when needed. Adds: - CLI: --pref name=value (repeatable, requires MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1) - Tools: set_firefox_prefs, get_firefox_prefs - restart_firefox: new prefs parameter for setting on restart - get_firefox_info: shows configured preferences Preferences are preserved across restarts and re-applied automatically.
After Firefox launches, sendBiDiCommand() was failing with "WebSocket is not open: readyState 0 (CONNECTING)" errors because it tried to send commands before the BiDi WebSocket connection was fully established. Add waitForWebSocketOpen() helper that: - Returns immediately if WebSocket is already OPEN (readyState 1) - Waits for 'open' event if CONNECTING (readyState 0) with 5s timeout - Throws immediately if CLOSING or CLOSED (readyState 2 or 3)
The pref tools checked process.env.MOZ_REMOTE_ALLOW_SYSTEM_ACCESS before calling getFirefox(), but the env var is only set in process.env during getFirefox() -> FirefoxCore.connect(). This caused tools to fail when launched with --env MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1. Remove early env checks and rely on the existing "No chrome contexts available" error which already provides helpful guidance.
Clean up test files by removing implementation-tracking comments that referenced plan steps (e.g., "// Step 1.1"). These were added during development and are no longer needed.
Highlight the browser.ml.enable preference as a practical example in both README and firefox-client.md. This pref is particularly relevant because RecommendedPreferences disables ML/AI features by default, making it essential for developing features like Smart Window with this MCP server.
Implement BiDi-native tools for installing and uninstalling Firefox extensions: - install_extension: Wraps webExtension.install BiDi command - Supports 3 types: archivePath (.xpi/.zip), base64, path (unpacked) - Firefox-specific moz:permanent parameter for signed extensions - uninstall_extension: Wraps webExtension.uninstall BiDi command Both tools provide straightforward access to Firefox's native WebDriver BiDi webExtension module functionality.
Implements extension discovery using chrome-privileged AddonManager API as a workaround for missing webExtension.getExtensions BiDi command. Features: - Lists all installed Firefox extensions with UUIDs and metadata - Extracts mozExtensionHostname (UUID) for moz-extension:// URLs - Shows background scripts, manifest version, active status - Distinguishes system/built-in vs user-installed extensions - Supports filtering by: ids (exact), name (partial), isActive, isSystem - Filters applied in browser for efficiency Requires MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1 environment variable.
Co-authored-by: Julian Descottes <jdescottes@mozilla.com>
Fixing some inconsistencies after rebasing the mozilla fork upstream as well as several cleanups: - stop referring to chrome context and prefer privileged context - remove md files which are not in english - update some urls from freema to mozilla
juliandescottes
force-pushed
the
rebase-upstream
branch
from
9b83e5a to
d604b6d
Compare
4 tasks
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
5 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
@freema
This PR merges all the changes from mozilla's initial fork of firefox-devtools-mcp. (
List of added features:
To avoid exposing new features to users, I added new cli flags.
--enable-scriptto enable all script evaluation tools. IMO should be safe to enable but was mentioned as a potential security issue in one .md file in the repo.--enable-privileged-contextto enable advanced features that typically require parent process / chrome privileges. This is mostly useful for internal Firefox development.I cleaned up and removed the non-english .md files. We can add the back if needed after translation?
And this doesn't include my work on the 100% BiDi-based version at the moment.
@padenot
Some notable changes compared to the version we are currently using internally: as mentioned above, will need 2 cli flags to have script evaluation + chrome scope. Also renamed "chrome scope/context" to "privileged scope/context" in most places to avoid confusion. The
--prefcli argument is no longer handled via chrome js, instead we use capabilities moz:firefoxOptions. This avoids restarting with chrome privs just for setting prefs.