I did some research and found the following tool set supports the scenario above and working fine in Firefox 19.0.2 (Linux):
- Scripted Code Editor: https://github.com/scripted-editor/scripted/
- Tile Tabs: https://addons.mozilla.org/en-US/firefox/addon/tile-tabs/ (Display tabs side-by-side)
- Auto Reload: https://addons.mozilla.org/en-US/firefox/addon/auto-reload/ (Reload page automatically when selected local files are changed)
Note: You need to unchecked "Reload active tab only" setting in AutoReload Preferences, otherwise auto reload will not work.