I reckon that since the new tab homepage add-on is not working you can remove it.
For some reason known only to Firefox developers (as far as I have been able to determine!) the about:home parameter setting is now defaulting to the original Firefox home page. So, for any future home page changes you might make within the latest Firefox version 27.0, it will require you to manually change the 'browser.newtab.url' to your desired home page address for new tabs.
As for 'what Plugins', the more usual plugins to have installed I would recommend Adobe Shockwave Flash, Sun Java, Microsoft Silverlight, Adobe Acrobat, Apple Quicktime and some Microsoft office plugins.
You could also consider installing a Macfee Site Advisor security extension that provides for a more secure surf and search experience. See:
http://www.siteadvisor.com/download/windows.html
The free version download link is located at the bottom of the MacAfee webpage. If you install it you will need to restart Firefox to complete and activate the package.
All depends on your surfing habits and as to what some web sites may require your browser to have in order to display the content. If you don't have the required plugin a website will usually inform you of the missing plugin.
Hope that helps.