Firefox theme plugin: correctly parse installations with multipe profiles (#626)

# Allows theming firefox/librefox installations with multiple profiles

The old code would incorrectly iterate over files (such as the
profiles.ini file) which would trigger an exception and skip the entire
firefox installation. This checks the path to ensure it is a directory
(and thus a profile) before trying to open the customChrome.css file for
writing. It correctly themes my Librefox now.

## Changelog

- Fixed path iteration

data/plugins/firefox_gnome_theme.py

@@ -118,11 +118,10 @@ class FirefoxGnomeTheme2Plugin(IPlugin):
                      "~/.var/app/org.mozilla.firefox/.mozilla/firefox",
                      "~/.var/app/io.gitlab.librewolf-community/.librewolf"]:
             try:
-                with (
-                    next(Path("firefox").expanduser().glob("*.*"))
-                    / "chrome/firefox-gnome-theme/customChrome.css"
-                ).open("w") as f:
-                    f.write(self.template.format(**self.variables))
+                for result in Path(path).expanduser().glob("*.*"):
+                    if Path.is_dir(result):
+                        with open(f"{result}/chrome/firefox-gnome-theme/customChrome.css","w") as f:
+                            f.write(self.template.format(**self.variables))
             except OSError:
                 pass
             except StopIteration: