Today we are shipping Nova with Firefox 157, the biggest refresh of the Firefox interface since Proton in 2021. The frame is cleaner, the sidebar plays a bigger role, and vertical tabs are now a first-class layout.
The good news: your theme still loads, and most color and image properties work as before. What changes is where some of them show up, especially around the sidebar and vertical tabs. Themes built around a background image are the most likely to look different.
We tested several popular themes ahead of the launch, but you know your theme best, so please install it in Firefox 157 and take a look.
We wrote up everything that changed, a short checklist of what to test, and the quick fixes for the most common issues on our blog.
If something still looks off after going through the checklist, reply here with a link to your theme and a screenshot. Those reports help us find the cases that need a fix in Firefox rather than in your theme.
The vertical-tabs change seems like the biggest thing theme developers should test, especially for themes that rely heavily on background images or specific layout assumptions. It’s good that the announcement asks developers to test their themes directly in Firefox 157 and report issues with screenshots, since that should help distinguish theme-specific problems from Firefox UI regressions.
A short checklist for the sidebar, vertical tabs, colors, and background positioning would probably make the testing process much easier for theme authors.
I have to ask. WHO asked for this change? I sure as heck didn’t. And I also have to say cramming it down our throats with having to actively hunt for a way to disable it, is no bueno. I’ve been using Firefox exclusively since 2004, and this, is not something people wanted. Stop enshittyfying Firefox. You don’t have to reinvent the wheel, just stop trying to.
Theme: Proton about:config - search for and disable everything NOVA. ← makes it looks normal and functional without bloat and COLORS ON AN EFFING BLACK DARK THEME.
In the blogpost I describe how you can bring the old view back, which is just with two clicks: For users who prefer the old look
Some of your users may miss Proton. From September 29, Mozilla is featuring a Firefox Proton theme in the Add-ons Manager for anyone who wants the previous look. It is a normal theme, so users can switch between it and yours at any time.
On a personal note, they didn’t ask me about this design update either, but I know a lot of market and user research goes into every major change.