how can I disable the browser's "Back" button in a HTML page?
In regular HTML page, is there any way to disable the back button in the toolbar?
You can't technically disable it, and moreover you shouldn't. Disabling the back button of a browser would fundamentally change the browsing experience for a user which isn't your place to do.
If going back in the browser creates problems for your application then you should restructure your workflow so it doesn't. An example of this is implementing the POST/REDIRECT/GET pattern.