Vertical tabs, tab groups getting way too big. Here are two of my own screenshots side by side, from 2025 vs 2026. There was a design change inbetween that made the tab groups even smaller but I couldn't find an image with that and had to go with this low-res one on the left. But that's the option I want back. The groups are there for me to revisit later, they don't need to take up so much space.
This is terrible forum software!, just awful, anyway, when the below stops working, (and it will):
URL bar -> about:config -> ENTER -> accept warning -> search nova ->
double-click line "browser.nova.enabled" to change to "false"
Do the below config change instead:
about:config ==> toolkit.legacyUserProfileCustomizations.stylesheets ==> true
Then create a userChrome.css file in this location below:
(create the chrome folder if it doesn't exist)
\Mozilla\Firefox\Profiles\xxxxxxxxxxxxx\chrome\userChrome.css
Insert below into userChrome.css, voilá excessively rounded corners gone! but not totally square either.
/* Nova Rounding Adjustments */
:root {
--border-radius-xsmall: 1px !important; /* Nova Default: 4px, Proton Default: 2px */
--border-radius-small: 2px !important; /* Nova Default: 8px, Proton Default: 4px */
--border-radius-medium: 3px !important; /* Nova Default: 12px, Proton Default: 8px */
--border-radius-large: 4px !important; /* Proton Default: 16px, [Undefined in Nova] */
--border-radius-xlarge: 6px !important; /* Nova Default: 24px, [Undefined in Proton] */
}
Then with the below skin, you will feel relieved as can be seen below.
https://addons.mozilla.org/firefox/addon/firefox-proton/
From this:
To this:
