500 JHtmlBootstrap

What version of Joomla are you using? From a quick search, it seems like that error is caused from either a) using a really old version of Joomla (like 3.0.2) and not Joomla 3.2.0+ or from a failed upgrade in the past. The startTabSet function is a core function of Joomla. If an upgrade didn't properly install/upgrade that file, my best suggestion would be to verify that you're on the latest or re-install all core Joomla files.

I hope that helps explain, but definitely let us know how we can help explain things better or if you think the above doesn't apply to you.

Thanks,
Alex

The 'core' files are the files that are installed by Joomla itself and required for it to function. The startTabSet function that's being reported as missing above should be in the file below:
/libraries/cms/html/bootstrap.php
That's a 'core' file of Joomla and if it doesn't exist, that function isn't in there, or it's not being loaded, it means there's something wrong with your Joomla installation. You'll need to determine what's wrong, or re-install Joomla.

I hope that helps, but if not, again, let us know what version of Joomla you are using.

Thanks,
Alex

cURL is a PHP addon. It's enabled by default, but some localhost environments (WAMP, MAMP) can disable them when installed. You'll need to edit the configuration of your localhost installation to re-enable cURL. The way to do that is specific to however you set your local server up though, so I can't really give you step by step instructions there.

cURL itself lets your site make outgoing connections to other servers. That's required by JFBConnect for all of our communication with each social network, and a vital part of our functionality.

I hope that helps explain,
Alex