To install UrlParams just go to the Download page
and download urlparams.xpi.
Then drag the file into Firefox or choose File->Open.
For Mozilla Users Only:
After installing UrlParams and restarting the browser, visit chrome://urlparams/content/lib/addpanel.xul
(copy/paste the link in Mozillas addressbar) and voila there is a new panel in Mozillas sidebar.
This must be done only once. On update you need not to do this again.
How to Install