cpan[3]> install WWW::Mechanize::Firefox
CPAN: Storable loaded ok (v2.20)
Going to read '/home/gurudutt/.cpan/Metadata'
  Database was generated on Mon, 02 Jul 2012 03:58:03 GMT
CPAN: LWP::UserAgent loaded ok (v5.834)
CPAN: Time::HiRes loaded ok (v1.9719)
Warning: no success downloading '/home/gurudutt/.cpan/sources/authors/
+01mailrc.txt.gz.tmp9571'. Giving up on it. at /usr/share/perl/5.10/CP
+AN/Index.pm line 225.
Fetching with LWP:
  http://www.perl.org/CPAN/authors/01mailrc.txt.gz
CPAN: YAML loaded ok (v0.71)
Going to read '/home/gurudutt/.cpan/sources/authors/01mailrc.txt.gz'
CPAN: Compress::Zlib loaded ok (v2.02)
......................................................................
+......DONE
Fetching with LWP:
  http://www.perl.org/CPAN/modules/02packages.details.txt.gz
Going to read '/home/gurudutt/.cpan/sources/modules/02packages.details
+.txt.gz'
^R
  Database was generated on Wed, 25 Jul 2012 06:14:33 GMT
..............
  New CPAN.pm version (v1.9800) available.
  [Currently running version is v1.9402]
  You might want to try
    install CPAN
    reload cpan
  to both upgrade CPAN.pm and run the new version without leaving
  the current session.


..............................................................DONE
Fetching with LWP:
  http://www.perl.org/CPAN/modules/03modlist.data.gz
Going to read '/home/gurudutt/.cpan/sources/modules/03modlist.data.gz'
......................................................................
+......DONE
Going to write /home/gurudutt/.cpan/Metadata
WWW::Mechanize::Firefox is up to date (0.66).

cpan[4]> install MozRepl::RemoteObject
MozRepl::RemoteObject is up to date (0.32).
[download]

I have installed firefox but there is no UI on this machine, so not sure how to install the plugin from browser.

Last I checked, firefox won't run without a UI, so you need a UI