I\'m using Firebug on Firefox 3.6.3 for Mac.
I want to use Firebug to view GET and POST parameters being passed. I have Firebug open at the Net > XHR tab. The panel say
Use the All tab in the NET panel
POST parameters can be seen in the NET panel. The first line is the page and if you click the down arrow to expand it, you can see the parameters under the section called "Post"
GET parameters can be seen in a similar way, on the expanded NET tab, its the section called "Params". Additionally, GET parameters will always be part of the url. It's the set of parameters after the ? in the URL.
Within Firebug you can also select DOM->document->forms->Your Form Name
All of you input variables and their post values will be listed under there.
I hope that helps.
Not sure how to do this in Firebug, but you could use Fiddler to see the entire request and response.