couple of questions after ML update (firewall,security preference,etc)

Hi, just updated from SL to ML a few hours ago, and got some questions

when I tried to install this currency converter widget, it says "Your security preferences allow installation of only apps from the Mac App Store and identified developers". Does this mean I can never download stuff from sites unidentified by Apple? and it says "YOUR security preferences", which means I must be able to change it right? How do i change it? And is there anything I should be careful about when changing these settings?

Another thing is about the Firewall, noticed it when i opened the security preferences. It seems like I can't switch on FileVault and Firewall by default or something (I don't really need FileVault,but just asking). Is it supposed to be like this? If so, I thought Firewall was supposed to basically protect you from potentially harmful sites, so why's it permanently switched off by default? Is it meant only for large networks that are very susceptible to these risky sites?

Following things are probably unimportant, but anyway wanted to ask
- When I opened Google Chrome first after updating it asked access to my Contacts, I guess this is probably because I had synced my old iPhone's contacts to Gmail......or is this something else I should be worried about?
- After fully charging and with the charger still connected, the battery percentage was 99% for a long time, is this just a bug or something minor, or can this mean my Mac battery's lifetime has actually decreased by 1%? Is this usual??
btw, thanks in advance for reading all this and replying

All legitimate Mac developers are registered with Apple, so this shouldn't be an issue. Most likely your currency converter widget hasn't been updated yet. It's no big deal. You can change the settings under "Security and Privacy" in the system preferences. Be aware that changing them to "Anywhere" opens to the door to potentially malicious malware.

Firewall should be turned off (as it is by default). The reason its off by default is that you already have a better hardware firewall doing that job -- it's called your router. The only time the software firewall should be turned on is when you're somewhere on some network that doesn't have a firewall. This is likely to be quite rare. Some people turn theirs on whenever they use a public network -- call me lazy, but that's too much work IMO, and again those places have a hardware firewall as well in most cases.

People think firewalls protect them from all kinds of stuff, and generally misunderstand firewalls entirely. Here's a good description of they do and don't do:
Security Awareness - Firewalls: What They Are, What They Can Do for You

And most of that only applies to Windows (the hacking, the viruses).

thanks for that
but I'm still not able to change those security settings for downloads. the options available are "Mac App Store" "App store & Identified Developers" and "Anywhere". The 2nd option seems to be ticked by default and I can't change it, I can only see it

from the given options it looks like the only way I can install any unidentified apps is by choosing "Anywhere". If I am able to change them, will it be safe to enable it temporarily when I need it and change it back afterwards? btw, the currency converter widget was an updated version,though not sure where it's from
Not having this widget isn't exactly the end of the world for me, but these security settings may give me problems in future for any other apps, how do I change them?

Also noticed the battery seems to be draining a little quicker, and the App Store sometimes takes really long to load some tabs. I guess it's too quick to judge coz it's been less than 24hrs since I started using ML, but are these things expected and/or temporary?