linux: fix Firefox settings not reverting #282

Improve the revert process for Firefox settings by extending
modifications to also include `prefs.js`.

- Validate profile directories similarly to execution script.
- Check and warn if Firefox is running during revert to prevent
  `prefs.js` from being overriden.
- Clarify output messages for execution and revert scripts.
- Add flowchart diagram for visual documentation.
- Improve documentation for consistency and precision.
- Update `.gitignore` to account for temporary draw.io files.

.gitignore

@@ -1,5 +1,13 @@
-node_modules
+# Application build artifacts
 /dist-*/
-.vs
+
+# npm
+node_modules
+
+# Visual Studio Code
 .vscode/**/*
-!.vscode/extensions.json
+!.vscode/extensions.json
+
+# draw.io
+*.bkp
+*.dtmp