One key reason why people use Vivaldi is the flexibility and customization. The Vivaldi User Interface lets you customize and move every part of its UI design. For example, you can move the address bar to the bottom, move tabs to the right, or even hide the entire UI if you choose to.

But where does all this customization come from? The developer of the Helium browser seems to have the answer. Vivaldi’s UI is basically a Chromium extension with special Vivaldi-only APIs and permissions. This discovery prompted a post on X, which you can view below.

i was curious about how vivaldi browser’s web ui works, and found out that all of the “vivaldi app” is a chromium extension with special vivaldi-only APIs and permissions
it's super cursed, but also somewhat genius, and explains how they're able to easily maintain it across…
— wukko (@uwukko) July 15, 2026

The extension ID for the UI is… “mpognobbkildjkofajifpdfhcoklimli.” The developer also joked that the extension name could’ve been made “prettier.”

While some people called this clever, others were rather surprised that the entire UI is just an extension. That would explain the bugs, how slow it could sometimes get, and there were plenty of complaints about the performance.

The question of importing this extension over to other browsers, to “turn them into Vivaldi,” was also discussed, but that’s not possible. It requires a lot of wiring, since it runs with Vivaldi-only APIs, and potentially some proprietary technology that’s difficult to replicate.

Following up on the original post, @uwukko also found that you could open the regular Chromium UI buried underneath the extension. Just pass the --disable-vivaldi argument (code), and it’ll just turn into a regular Google Chrome-style UI. You can view the image below for reference.

Since I’m on macOS, I ran the command below in the Terminal:

--disable-vivaldi

Sure enough, this completely disabled the custom UI and returned a basic Google Chrome look. The first image I’ve attached shows the usual design, and the second image shows the UI after disabling the extension.

Note: We’re not claiming that Vivaldi is scamming users here, since using a custom Chromium extension actually simplifies the browser maintenance process. Vivaldi’s method makes it much easier for the team to add new features and keep the browser updated without breaking things.

So, if you’re a Vivaldi user, does this affect you? Not directly, at least. However, since most of the performance issues and bugs can be attributed to the extension, the browser does need optimization and refinement nonetheless.

In other Vivaldi news, we recently received clarification on what’s happening to uBlock Origin and other MV2 extensions. More on that here.

The post Turns out Vivaldi’s entire interface is secretly just a Chromium extension appeared first on PiunikaWeb.