The accepted answer is great, but I wanted to add more details in case your browser loads other files from extensions outside of "React Dev Tools" that you don't recognize.

In the network tab (the OP posted a screenshot) you can click on the request to see the details of the request.

Note that this URL specifically uses thechrome-extensionprotocol, which is our hint that it is a Chrome extension:

chrome-extension://fmkadmapgofadopljbjfkapdkoienihi/build/installHook.js

Please note the identifier in the previous URL: "fmkadmapgofadopljbjfkapdkoienihi". How do you know which Chrome extension the identifier refers to?Copy the identifier to the clipboard. Visit

chrome://extensions/

in Chrome and paste the identifier into the search input at the top of the page. You'll notice that the search results have been filtered to show which extension is loading the file.You can disable the extension by toggling the slider or delete it by clicking the Remove button.

If you click the "Details" button on a specific extension in the

chrome://extensions

window, Chrome should load a specific details page and reiterate that identifier. In this example, Chrome loads the URL:

chrome://extensions/?id=fmkadmapgofadopljbjfkapdkoienihi

...Note that the identifier "fmkadmapgofadopljbjfkapdkoienihi" appears again.

Note other ways to disable extensions, such as

Running Chrome with extensions disabled

with the--disable-extensionsor--incognitoflag

In my case, installHook.js came from the React Dev Tools Chrome extension. You don't need to worry about this as it won't impact application performance for end users.