Question: I received a new iPhone yesterday and connected it to my home Wifi network.

On content heavy sites it runs perfectly fine, but if I use either the Youtube site or the Youtube app I can't watch anything. It takes forever to watch 5 seconds of video.

My first question is, how can I be sure that my phone is using local Wifi for the internet connection and Youtube app (it says connected in the settings, but is there an icon in the display etc. to confirm Wifi connection)?

Any suggestions as to why Youtube runs slow when other heavy sites load without problem?

Answer: 
Yes, you can have both versions. In fact you can install the new Firefox in your home directory's Application folder (and it will be only accessible with your account). If you don't have ~/Applications folder, you can create it (and Finder will mark it with the same icon as the /Applications one). Note that you cannot use both versions simultaneously. You can also rename the Firefox.app to Firefox 4.app, and install it in /Applications - it'll work flawlesly.

ps. I prefer the first method - Install applications that I'm testing in my home Applications folder, and when I'm sure they're ok, move them/replace application in /Applications.
[OS X: Install and Run Firefox 3 and Firefox 4 on the Same Computer | Mozilla Firefox | Tech-Recipes](http://www.tech-recipes.com/rx/2828/os_x_install_firefox_2_firefox_3_same_computer/)

Or just make copies of `~/Library/Preferences/org.mozilla.firefox.plist` and `~/Library/Application Support/Firefox/`.