They are actually called vendor prefixes, and there some more actually
-o- Opera
-ie- Internet Explore
You can use
http://caniuse.com/#search=gradient to see if you need a vendor prefix for you rule, often it is just common sense to include all vendor prefixes, as you want to support older browsers.
I might wanna have a look at Compass with Sass, which got mixins that produces all vendor prefixes for you.
If you are on a Mac or Linux machine, you can install it through gem (
http://compass-style.org/) (Sass
http://sass-lang.com/)
gem install compass
When install you can go to you project folder an write
compass init
Which will initialize some structure and stylesheets for you, and finally
compass watch
Which looks for changes in your scss files, and compiles them directly to coresponding css file.
Hope it helps
.