I’ve been using vertical tabs for a while, and I do think that the round icons are 1: better suited to the design of the majority of favicons, and 2: offer a quicker visual separation at a glance. It’s easier to distinguish between tabs.

If you prefer horizontal tabs, the rounded tabs with a light stroke are even more stark. Firefox has long had a problem with the visual language of the tabs. It has been hard to clearly distinguish between active and background tabs. If you were not already familiar with the color scheme, and someone showed you a window with two tabs, you’d have to make a wild guess to know which was the active tab. Chrome for example represents this by connecting the active tab to the window view - immediately clear. The old Firefox tabs were ambiguous because they didn’t connect, and they also weren’t clearly separated. This design makes a clear commitment.

The new app icons are gorgeous. The design looks more coherent across the app. It manages to be modern and clean, while presenting a characteristic personality. For too long, Firefox has been chasing trends and aiming for a middle that doesn’t exist. Firefox is different and should look different. I think it’s much better to make a visual statement that not everyone will love than to have no perspective at all.

Some people have railed against the new default theme. It’s not for everyone, but there are 1000s of official and user-created themes to choose from. I have been using a custom theme for ages precisely because the old default theme was ugly.

A small addition, I use Firefox as my default PDF viewer. The new viewer has a few minor improvements and fixes one or two past missteps. I’m sure folks will (rightly) say there are better options for a PDF viewer, but it meets my needs.