Pass a variable via url during development

When debugging an app I’d like to be able to quickly change some startup values by changing the url. For example, when I run an app in Flex, it opens a url like this:

file:///somepath/GameClient/bin-debug/GameClient.html

I’d like to be able to change the url to this:

file:///somepath/GameClient/bin-debug/GameClient.html?myvar=myval

then reload the page and have my app pickup the variable. What’s the best way?