Pass query string to Webform text field
You can set a default value for each field on your webform.  The default value you would use would be 

For Webform v3 and under:

%get[customer_name]


For Webform v4+:

[current-page:query:customer_name]


To get a first and last name you could do something like:

URL:

http://mysite.com/myform?first_name=John&amp;last_name=Doe


First Name Default Value:

%get[first_name]                 //webform &lt;= v3
[current-page:query:first_name]  //webform &gt;= v4


Last Name Default Value:

%get[last_name]                 //webform &lt;= v3
[current-page:query:last_name]  //webform &gt;= v4