firefox: fixed by removing enabling of invalid extensions (see note)

Note:

Following is a snippet from the build log:
----------------------------------------------------------------------------
configure: warning: auth is no longer an extension, use --disable-negotiateauth to disable.
configure: warning: cookie and permissions are no longer extensions, use --disable-permissions to disable.
configure: warning: pref is no longer an extension, use --disable-pref-extensions to disable.
configure: error: Unrecognized extension provided to --enable-extensions: xml-rpc.
configure: error: Unrecognized extension provided to --enable-extensions: xmlextras.
configure: error: Unrecognized extension provided to --enable-extensions: transformiix.
configure: error: Unrecognized extension provided to --enable-extensions: webservices.
----------------------------------------------------------------------------

www/firefox/firefox.conf

@@ -27,7 +27,7 @@ mk_add_options MOZ_PHOENIX=1
 
 ac_add_options --disable-mailnews
 ac_add_options --disable-composer
-ac_add_options --enable-extensions=default,cookie,permissions,xml-rpc,xmlextras,pref,transformiix,webservices,auth
+ac_add_options --enable-extensions=default
 ac_add_options --enable-mathml
 ac_add_options --enable-crypto
 ac_add_options --enable-module=psm