Browser plugins are programs/software that expand the functionality of browsing by adding few program such as media player (for playing any format of file), photo editor (for enhancing quality or viewing all formats).

2. Browser plugins are programs/software that expand the functionality of
browsing by adding few program such as media player (for playing any
format of file), photo editor (for enhancing quality or viewing all formats).
These programs are offered by third party rather than developer of
browser to enhance the accessibility of browser. Since, these plugins are
not designed by developer hence they need to be installed.

3. Legitimate browser plugins: These are browser plugins, that facilitate folks
by adding specific feature to associate in nursing existing application
program. They're harmless and user friendly.
E.g. Google toolbar, MSN Search toolbar, Adobe athlete Reader.
Malicious browser plugins: It's malware that doesn't unfold like another
malicious malware. They're harmful and will cause undesirable and unsafe
actions like obstruction in access to page that you just truly request to
succeed in.

6. http://how-to-remove.org/malware/browser-plugin-malware-removal/

7. http://how-to-remove.org/malware/browser-plugin-malware-removal/