https://gist.github.com/paulirish/78d6c1406c901be02c2d
Option 1: Command-line download extension as zip and extract
extension_id=jifpbeccnghkjeaalbbjmodiffmgedin # change this ID
curl -L -o "$extension_id.zip" "https://clients2.google.com/service/update2/crx?response=redirect&os=mac&arch=x86-64&nacl_arch=x86-64&prod=chromecrx&prodchannel=stable&prodversion=44.0.2403.130&x=id%3D$extension_id%26uc"
unzip -d "$extension_id-source" "$extension_id.zip"
Thx to crxviewer for the magic download URL.
Option 2: Use the CRX Viewer extension
The Chrome extension source viewer is open source (github repo) and makes this super easy.
Option 3: View source of locally installed extension
Find your Chrome local profile directory. Open chrome://version/ and find the "Profile Path:` field. Open that folder up.
Open the Extensions/ subfolder
All your extensions are here, with typically readable source.
Mapping between locally installed extension IDs and names
On about:extensions, turn on Developer Mode and you'll see IDs under each entry
Inside the Extensions/ folders, the manifest.json has a readable name field
image