View and modify form data before posted to server

Question

There is a website I need to report data on a daily basis. To report the data I need to fill out a form and submit (post) it.

One of the fields is a select element, and it's missing a value. The value that's missing is accepted by the server, but not yet implemented in the GUI (website).

Is there a possibility to edit the post data before it gets submitted to the server?

Solution

If it's POST then you can use the Firefox Tamper Data extension to intercept the request and modify the POST parameter values before sending it on.

https://addons.mozilla.org/en-US/firefox/addon/tamper-data/

The extension is a bit fiddly to get going on Firefox 29+, you need to install it, then hit Alt to access the menu bar, then go to Tools -> Tamper Data.

This will bring up a new window for Tamper Data. Fill out your form, but before you submit, click 'Start Tamper' in the Tamper Data window, then submit the form. Tamper Data should pop up a dialog asking if you want to tamper, click the 'Tamper' button and a new window containing the details of the request will appear. On the right hand side you should see your POST parameters and be able to edit their values. Click OK to submit the modified request to the server, then click 'Stop Tamper' in the Tamper Data menu.

Comments

[CoderGuy123]

Note: does not work for FF Quantum (per 2017-12-05).

[Jānis Elmeris]

@Deleet, why does it not work?

[ccpizza]

the extensions works, but it does not 'tamper' anything, i.e. there is no way to modify the parameters — they are read-only