Want to copy it to another system (not browser) without downloading it again...
Your user data can be found depending on your OS in the following directories:
Windows 7 (probably vista as well)
Mac OS X: /Users/YourUserName/Library/Application Support/QuakeLive/quakelive/
You should be able to run in multiple browsers without re-downloading the data. You only need the plugin for the browser you are using, which is ~6MB download.
For Windows 7, you can access the folder easiest by clicking the Windows Start Icon (at the bottom-left of your PC screen), and typing the following (or copy-and-pasting) into the search field:
In the AppData folder, it looks like this:
You can find many application folder in one of these folders.
For example, the Google Chrome folder is found in:
For future reference, the AppData folder is located in your usersname folder (where downloads and documents and pictures folders are), but it is a hidden folder.
You can turn on hidden folders to be visible by doing the following:
Hope this helps! Good luck!