It’s been a long-running feud: Microsoft, with Windows’ dominant market share, and browser makers fighting for every megabyte of user attention. Over the years, Microsoft has developed an arsenal of “manipulative design tactics” to keep you locked into its own offerings—Edge and Bing—often at the expense of your choices. From “malware-like” pop‑ups warning you of phantom risks when downloading Chrome, to hijacking file‑opening behaviors across Windows features, Microsoft has perfected the art of the nudge…and sometimes the shove. Now, Opera has had enough. In a bold move, the Norwegian browser maker dropped a formal competition complaint this week with Brazil’s antitrust regulator, CADE.

“Microsoft thwarts browser competition on Windows at every turn,” says Aaron McParlan, Opera’s general counsel. “First, browsers like Opera are locked out of important preinstallation opportunities. And then Microsoft frustrates users’ ability to download and use alternative browsers.”

Microsoft’s tactics can be boiled down to two key strategies. First, you simply can’t escape Edge: it’s pre‑installed everywhere, from brand‑new PCs to system folders. Second, when you try to break free by downloading—or even searching for—another browser, you’re met with on‑screen barriers: banners discouraging you, pop‑ups claiming “you’re safer with Edge,” or even websites that mysteriously block alternative browser installers. According to Opera’s complaint, these “dark patterns” go so far as to override your chosen default browser when opening PDFs, email links in Outlook, Teams chats, or when you click links inside Windows Search and Widgets.

Opera highlights an egregious example: search for “download Chrome” in Edge, and you’ll get an “obtrusive banner” telling you that “Switching browsers can put you at risk,” complete with Microsoft’s security seal. Contrast that with the plain‑spoken download links you find on Chrome’s official site—and you begin to see how the playing field is tilted.

Opera’s decision to take the fight to Brazil isn’t random. The country is one of Opera’s strongest markets—it holds nearly 7% of desktop browser share there (compared to Edge’s roughly 11.5% and Chrome’s whopping 75%). “Opera is already a major success in Brazil: it is the third most popular browser in Brazil and has millions of loyal users who actively choose it, despite Microsoft’s tactics,” McParlan notes. By challenging Microsoft before CADE, Opera hopes Brazil can set an international precedent that reigns in global “manipulative design” practices.

Opera’s Brazil complaint is the latest chapter in a saga that dates back nearly two decades. In 2007, Opera filed a landmark antitrust complaint with the European Commission, accusing Microsoft of bundling Internet Explorer into Windows—effectively locking out competitors. That case ultimately led to the introduction of the “browser ballot screen,” allowing Windows users in Europe to choose among a dozen major browsers instead of being auto‑defaulted to Internet Explorer. Microsoft was even fined €561 million in 2013 for failing to include this ballot in Windows 7 Service Pack 1.

Fast‑forward to last year, and Opera again pressed regulators under the EU’s new Digital Markets Act (DMA), seeking to have Edge designated as a “gatekeeper” service. Although the European Commission declined that designation, it still imposed several changes on Windows to make switching browsers less painful—changes that Opera deemed “insufficient.” Hence, the EU complaint is on appeal before the European courts.

If CADE finds merit in Opera’s allegations, Opera is seeking sweeping remedies:

• Pre‑installation rights: PC manufacturers must be free to preload any browser as the default, not just Edge.
• No more download blocks: Microsoft must cease its pop‑ups, banners, and UI tricks that discourage downloading rival browsers.
• Ban on dark patterns: Clear rules against manipulative design tactics that steer users toward Edge.
• OEM incentives removed: Prevent Microsoft from tying Windows OS rebates to the requirement that devices ship in “S mode”—a configuration that locks you into Edge and the Microsoft Store.

It’s not just about window‑shoppers being bombarded with Edge ads. Earlier this year, Microsoft even created a spoofed Google‑style interface for Bing, complete with a fake “Google Doodle” and search bar—in an apparent bid to trick users into thinking they were on Google Search. Once the community noticed, Microsoft quietly pulled the plug.

This battle isn’t just a browser war; it’s about user agency in digital markets. Dark patterns, deceptive UI, and restrictive OEM agreements are cropping up in streaming services, app ecosystems, and smart‑device hubs. The outcome of Opera vs. Microsoft in Brazil could ripple outward, shaping how regulators worldwide address digital consumer choice.