Why isn't the developer mode showing up on a particular VF page?

Question

For some VF pages, the Developer mode is showing, and others it isn't. What's causing that? I'd like the dev mode to show

https://developer.salesforce.com/docs/atlas.en-us.pages.meta/pages/pages_tools_edit_toolbar.htm

Answer 1

When you are in a Visualforce Page see the URL in the address bar and if you see this query string parameter in the url

core.apexpages.devmode.url=1

the development mode will be disabled for that page

I am not sure why you get that for certain pages but if its there in the URL, remove it from the url and try..

Answer 2

Navigate to the Advanced User Details (User Setup Page) for the current user and enable "Development Mode". You already have the steps outlined in the link that you've posted. Read the "To enable the View State tab:" section