feat(firefox): new tab background follows the wallpaper

FF Ultima selects the new tab image from a fixed list by pref. Its
darknix.png slot is now a link to ~/.cache/udt/wpaper, so selecting it
once in about:config makes the new tab show the current wallpaper, and
Firefox picks up a change without a restart.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

2 files changed, 16 insertions, 0 deletions

diff --git a/AGENTS.md b/AGENTS.md
index e874127..c1ab004 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -270,6 +270,13 @@ the terminal palette follows the scheme and never the wallpaper. The
 write lands after `wallp` has already run `wal --theme`, so it wins; reorder
 those two and pywal's wallpaper-derived colours come back.
 
+Firefox's new tab shows the wallpaper itself, not a colour. FF Ultima picks
+the new tab background from a fixed list of images by pref, and `install.sh`
+links its `walls/darknix.png` slot to `~/.cache/udt/wpaper`; selecting it once
+(`user.theme.wallpaper.darknix` in `about:config`) is the only manual step.
+Firefox revalidates the file on each new tab, so a wallpaper change reaches a
+running browser without a restart.
+
 Not everything tracks the wallpaper. rofi, quickshell, Hyprland borders,
 hyprlock's border (through `~/.cache/udt/hyprlock-border.conf`), Sublime's
 colour scheme, Firefox, GRUB, the homepage and the AK820 Pro keyboard do; conky, Qt, GTK, waybar, hyprlock's panel palette
diff --git a/install.sh b/install.sh
index 7a78f80..b0fd835 100755
--- a/install.sh
+++ b/install.sh
@@ -123,6 +123,15 @@ fi
 mkdir -p "$HOME/.cache/wal"
 ln -sfn "$HOME/.cache/udt/colors.json" "$HOME/.cache/wal/colors.json"
 
+# Firefox's new tab background. FF Ultima picks it from a fixed list of
+# images by pref; its darknix.png slot is pointed at the wallpaper udt-accent
+# tracks, so selecting it once (user.theme.wallpaper.darknix in about:config)
+# makes the new tab follow every wallpaper change. Skipped per profile
+# without FF Ultima.
+for walls in "$HOME"/.mozilla/firefox/*/chrome/theme/color-schemes/walls; do
+    [ -d "$walls" ] && ln -sfn "$HOME/.cache/udt/wpaper" "$walls/darknix.png"
+done
+
 # The rofi menus are bound by name in hypr-theme's keybindings, so they keep
 # the names they had when they lived loose in ~/bin.
 for f in udt-accent udt-grub udt-keyboard udt-steps udt-palette udt-machine-name udt-powermenu.sh udt-launcher.sh qar-scrotmenu.sh; do