Browser seems to automatically add 'nofollow' to links, even though it's not in the page source

Question

I've noticed every rel="noopener noreferrer" link with target="_blank" we add to our sites automatically also get a 'nofollow' added to the rel attribute, when I inspect them in dev tools. I'm pretty sure it has to be added by the browser, because when I check the page source in the browser, only noopener and noreferrer are there.

I mainly use Brave on MacOS, but Chrome, Firefox and Safari show the same behaviour.

What could cause this?

EDIT: It turned out to be a JavaScript script adding it whenever I used target="_blank".

Answer 1

As this is happening across all browsers I'd say it's unlikely a browser extension is doing this. Although still check if it happens with any turned off.

Failing that, it may be that the site is adding the nofollow via JavaScript that is client side rendered. Thus why you don't see it when viewing source, but do when inspecting element.

In Google Search Console, you could inspect the live page and check the rendered HTML in there to see what GoogleBot is seeing. Although if its via JavaScript it may not pick it up.

You could as use a tool such as Screaming Frog to crawl the page and then check the HTML in both text rendering and also in JavaScript rendering.

If you find the nofollow, you'll know its your site adding it, rather than your browser.