For anyone that is doing web design/development I would highly recommend this add-on for Firefox. Most helpful thing I've found lately.
Web Developer (https://addons.mozilla.org/en-US/firefox/addon/60)
I use it quite a bit - it's fantastic. Has several bugs which are covered over at the developer's website. A big one is the disappearance of background images declared in the CSS when you're using the CSS editor. That alone almost cripples my attempts at doing live editing of the CSS.
I tried to download the firefox addon Web Developer and I got an error message and I don't know how to proceed. add the steps of downloading web developer.
I still use this regularly in addition to Firebug.
Downloaded via Firefox add-on manager for me. I too use it all of the time.
ok, noob time here...
what is this used for?
how does it help you?
Can you tell I know nothing about web dev?
It's an add-on for firefox that will show you a lot of relevant info about objects on a web site. Colors, images, CSS, etc...
I was reading about the "User Agent Switching". Is this something that's done pretty regularly, or is it just for hackers that want to spoof a browser?
Yes it is fairly regular. Most web sites probably already do this every time you visit their site. I used to do it here until the mod quit working that determined if you were using a mobile browser.