Modify URL before loading page in firefox

Question

I want to prefix URLs which match my patterns. When I open a new tab in Firefox and enter a matching URL the page should not be loaded normally, the URL should first be modi

Answer 1

Is it possible to modify an URL through a Mozilla Firefox Addon before the page starts loading?

YES it is possible.

Use page-mod of the Addon-SDK by setting contentScriptWhen: "start"

Then after completely preventing the document from getting parsed you can either

1. fetch a different document from the same domain and inject it in the page.
2. after some document.URL processing do a location.replace() call

Here is an example of doing 1. https://stackoverflow.com/a/36097573/6085033