Anyone can ship a ModHeader replacement with AI now. That's the scary part.

A developer shipped a ModHeader replacement browser extension in a single weekend, with an AI agent writing roughly 16,000 lines of extension code and 23,000 lines of tests, after Google and Microsoft pulled the original 1.6-million-install header editor in July over a hidden browsing-history collector. The developer argues that because AI coding agents never refuse requests for broad permissions or telemetry, the security of such extensions now rests on a developer's judgment rather than the cost or effort of writing the code.

Quick recap if you missed it. In July, Google and Microsoft pulled ModHeader, the header-editing extension with 1.6 million installs, after researchers found a browsing-history collector hiding in the code it was switched off . The switch was an empty array that any routine update could have filled. Your browser would have just installed it one afternoon like any other version bump. Within a few weeks, at least six "safe alternatives" showed up. Different names, same blog post. I know, because I just shipped one too. Here's what nobody in that pile is saying out loud: in 2026, building something like a header extension is almost free assuming you know how to manage your tokens . I'd love to tell you mine took months of craftsmanship. It took a long weekend, and an AI agent wrote nearly all of it. About 16,000 lines of extension, 23,000 lines of tests. Started on a Friday, in the store on Monday. If I can do that, so can anybody, including whoever buys a tired extension next year and wants to "add monetization." So the question "which replacement is safe" has somewhat changed meaning. It used to be about who wrote the code... Now the code is the cheap part. What you're actually betting on is the person's judgment , and whether they bothered to make that judgment permanent. The AI said yes to everything Something I learned fast is that the agent never says no. Ask for telemetry, you get telemetry, nicely typed. Ask for "all sites" access because it's simpler, you get it, with a helpful comment. At one point it gave the extension standing access to a license server host, because convenient. Convenient is exactly how ModHeader's story starts. I pulled it out and added a rule so it can't come back. That was the whole job, really. Looking back at my time log, writing code was about a third of the hours. The other two thirds were tests, reviews, and fixing what the reviews found. I kept a decisions file. It has 160 entries. Most of them are a version of "no": connect-src 'none' , so the browser refuses any request it might ever try to make. None of this is clever. A good developer would have done it on a Tuesday before they were done with their morning coffee. The point is that the AI would have happily done the opposite, and the result would have looked identical in the store listing. Same screenshots, same "we respect your privacy" paragraph. ModHeader's listing said that too. What the studies keep bumping into There's a growing pile of research on AI and developers, and it's contradictory on speed. Faster for juniors, slower for seniors on big codebases, then faster again a year later. But one finding keeps coming back from different directions. Stanford's team tracking around 120,000 developers found the gap between AI-using and non-AI teams widening over two years, and that the gains correlated with how clean the codebase already was. A Microsoft Research study on teams adopting coding agents found the ones that were already fluent got faster, the others barely moved, and both ended up with more complex code. In other words: AI doesn't hand out judgment . It multiplies whatever was already there, including nothing. For most software that's a productivity debate. For browser extensions it's a security property. An extension is dangerous in proportion to what it's allowed to do, and its code can change under you without asking. The only thing standing between you and the next ModHeader is a stranger's taste in saying no. Now that stranger ships in a weekend. The 10-second version You can't audit every extension, and you shouldn't have to. Two things get you most of the way. First, read the install dialog. If it opens with "Read and change all your data on all websites," you're not just trusting this developer, you're trusting whoever has the account in two years. For a header editor that grant isn't necessary anymore; Manifest V3 lets it ask per site. Second, if the maker is reachable, ask one question: what can't your extension do, and what stops an update from changing that? Promises are the wrong answer. "We would never" is what every listing says. The right answer sounds like a mechanism: a policy the browser enforces, a permission it never asked for, a build that fails. That's the standard I'd hold mine to as well. It's called Wirelet ; the install dialog asks for no sites, and if you find something that doesn't match this post, tell me. I'd rather fix it than write the seventh "safe alternative" post.