Does Firefox DevTools MCP work with ChatGPT (Codex)?
Yes. Firefox DevTools MCP passed every step of our test in ChatGPT (Codex) on Oct 23, 2026: it installed, connected, its tools were visible, and an agent used it to finish a real task.
Result
Steps
- install OK
- connect OK
- tools visible OK
- agent task: click reveal OKnavigate + interact + read back. The code is computed by page JavaScript only after the click.
From our own harness run, not the maker’s claims. How we test.
Versions tested
Codex CLI 0.162.0-alpha.17.2 · @mozilla/firefox-devtools-mcp 0.10.6 · connect time not recorded · tested Oct 23, 2026
Server package tested: @mozilla/firefox-devtools-mcp 0.10.6 (npm, Node v20.19.2; resolved 2026-10-23)
Direct and key dependencies as resolved: @modelcontextprotocol/sdk 1.29.0 · express 5.3.0 · geckodriver 6.0.2 · selenium-webdriver 4.36.0 · ws 8.21.0 · yargs 17.7.2 · zod 4.6.7 · zod-to-json-schema 3.25.2
All 136 resolved dependencies
@bazel/runfiles==6.5.0
@hono/node-server==1.19.17
@modelcontextprotocol/sdk==1.29.0
@wdio/logger==9.29.1
@zip.js/zip.js==2.24.0
accepts==2.0.0
agent-base==7.1.4
ajv==8.20.0
ajv-formats==3.0.1
ansi-regex==5.0.1, 6.4.0
ansi-styles==4.3.0
body-parser==2.4.0
bytes==3.1.2
call-bind-apply-helpers==1.0.2
call-bound==1.0.4
chalk==5.6.2
cliui==8.0.1
color-convert==2.0.1
color-name==1.1.4
content-disposition==2.0.1
content-type==1.0.5, 2.1.0
cookie==0.7.2
cookie-signature==1.2.2
core-util-is==1.0.3
cors==2.8.6
cross-spawn==7.0.6
debug==4.4.3
decamelize==6.0.1
depd==2.0.0
dunder-proto==1.0.1
ee-first==1.1.1
emoji-regex==8.0.0
encodeurl==2.0.0
es-define-property==1.0.1
es-errors==1.3.0
es-object-atoms==1.1.2
escalade==3.2.0
escape-html==1.0.3
etag==1.8.1
eventsource==3.0.7
eventsource-parser==3.1.1
express==5.3.0
express-rate-limit==8.7.1
fast-deep-equal==3.1.3
fast-uri==3.1.9
finalhandler==2.1.1
forwarded==0.2.0
fresh==2.0.0
function-bind==1.1.2
geckodriver==6.0.2
get-caller-file==2.0.5
get-intrinsic==1.3.0
get-proto==1.0.1
gopd==1.2.0
has-symbols==1.1.0
hasown==2.0.4
hono==4.13.13
http-errors==2.0.1
http-proxy-agent==7.0.2
https-proxy-agent==7.0.6
iconv-lite==0.7.3
immediate==3.0.6
inherits==2.0.4
ip-address==10.7.4
ipaddr.js==1.9.1
is-fullwidth-code-point==3.0.0
is-promise==4.0.0
isarray==1.0.0
isexe==2.0.0
jose==6.2.13
json-schema-traverse==1.0.0
json-schema-typed==8.0.2
jszip==3.10.2
lie==3.3.0
loglevel==1.9.2
loglevel-plugin-prefix==0.8.4
math-intrinsics==1.1.0
media-typer==1.1.1
merge-descriptors==2.0.0
mime-db==1.54.0
mime-types==3.0.2
modern-tar==0.3.5
ms==2.1.3
negotiator==1.1.0
object-assign==4.1.1
object-inspect==1.13.4
on-finished==2.4.2
once==1.4.0
pako==1.0.11
parseurl==1.3.3
path-key==3.1.1
path-to-regexp==8.4.2
pkce-challenge==5.0.1
process-nextick-args==2.0.1
proxy-addr==2.0.8
qs==6.16.1
range-parser==1.3.0
raw-body==3.0.2
readable-stream==2.3.8
require-directory==2.1.1
require-from-string==2.0.2
ret==0.5.1
router==2.2.0
safe-buffer==5.1.2
safe-regex2==5.1.2
safer-buffer==2.1.2
selenium-webdriver==4.36.0
send==1.2.1
serve-static==2.2.1
setimmediate==1.0.5
setprototypeof==1.2.0
shebang-command==2.0.0
shebang-regex==3.0.0
side-channel==1.1.1
side-channel-list==1.0.1
side-channel-map==1.0.1
side-channel-weakmap==1.0.2
statuses==2.0.2
string-width==4.2.3
string_decoder==1.1.1
strip-ansi==6.0.1, 7.2.0
tmp==0.2.7
toidentifier==1.0.1
type-is==2.1.0
unpipe==1.0.0
util-deprecate==1.0.2
vary==1.1.2
which==2.0.2
wrap-ansi==7.0.0
wrappy==1.0.2
ws==8.21.0
y18n==5.0.8
yargs==17.7.2
yargs-parser==21.1.1
zod==4.6.7
zod-to-json-schema==3.25.2Captured with: npm ls --all --json in the npx env.
What happened in this run
Install config we used
[mcp_servers.firefox-devtools-mcp]
command = "npx"
args = ["-y", "@mozilla/firefox-devtools-mcp@latest", "--headless", "--viewport", "1280x720"]Connection check
server answered tool calls during the taskTools check
verified via task step: agent saw and called the server's tools
Agent task: click reveal
- Tool calls, in order:
firefox-devtools-mcp:new_page,firefox-devtools-mcp:take_snapshot,firefox-devtools-mcp:click_by_uid,firefox-devtools-mcp:get_page_text
Raw details from our harness log for this run. Secrets redacted.
Set it up in ChatGPT (Codex)
Copy-paste config for every app is on the Firefox DevTools MCP page. Not connecting? ChatGPT (Codex) MCP troubleshooting.
Other apps we tested it in: Claude Code (passed) · Cursor (passed).