diff --git a/.config/bash/module/rust.sh b/.config/bash/module/rust.sh
new file mode 100644
index 0000000..ad44ab9
--- /dev/null
+++ b/.config/bash/module/rust.sh
@@ -0,0 +1,2 @@
+# Open Rust book.
+alias rust_book="rustup docs --book"
diff --git a/.local/share/flatpak/overrides/org.mozilla.firefox b/.local/share/flatpak/overrides/org.mozilla.firefox
index a3c71bd..6ed1ed1 100644
--- a/.local/share/flatpak/overrides/org.mozilla.firefox
+++ b/.local/share/flatpak/overrides/org.mozilla.firefox
@@ -1,3 +1,3 @@
 [Context]
 devices=dri
-filesystems=!xdg-download;~/tmp;~/download;~/.mozilla
+filesystems=!xdg-download;~/.rustup:ro;~/download;~/.mozilla