Sometimes you may need special Firefox profile for development purposes if you for example are debugging your extension.
In this case you may want to have simultaneously opened two instances of firefox: one with your bookmarks and all staffs and another, light but with dev extensions and any other features, it is possible.
1. Create new profile "Dev" by command
"C:\Program Files\Mozilla Firefox\firefox.exe" --profilemanager
2. Create shortcut for your profile
"C:\Program Files\Mozilla Firefox\firefox.exe" -P "Dev" -no-remote
3. Install some useful extensions:
3.1. Restart Firefox
3.2. Firebug
4. Setup your development environment for this profile