WordPress is fun but adding a new theme or plugin to your WordPress installation is not - you have to download the WordPress Theme or Plugin from the developer's website to your hard-drive, unzip the files and then upload them to the right WordPress folder via FTP.
You follow the same cycle when installing new updates to your existing WordPress themes or plugins.
Well, here's a neat solution to make your WordPress life a bit simple - OneClick Firefox Extension - that allows you to install (or update) new WordPress themes and plugins via Firefox.
You just have to right-click the URL on a webpage that points to zipped WP theme or plugin and select Install from the contextual menu. Then you enter your WordPress dashboard and activate the plugin. That's it.
Think of OneClick as a simple replacement of your FTP client - it takes the zipped installer files for themes or plugins from the developer's site and unzips them to the appropriate folder of your WordPress installation.