docs: replace firefox with zen

Author: openscript

src/content/notes/tools/software.en.mdx

@@ -23,7 +23,7 @@ I'm using [Arch Linux](https://archlinux.org) with:
 
 - [LibreOffice](https://libreoffice.org) as office suite.
 - [Visual Studio Code](https://code.visualstudio.com) as code editor.
-- [Firefox](https://www.mozilla.org/en-US/firefox) as web browser.
+- [Zen Browser](https://zen-browser.app/) as web browser.
 
 ## Android