There are certain addons for almost all common web browsers to ignore these CORS-errors and allow those requests even if there is no security header present. For testing purposes in my projects I’m using the “Moesif Origin & CORS Changer” addon, which is available in the Chrome addon store. It either allows to deactivate CORS-checks as a whole or on specific web pages (e.g. localhost).

How to personalize web pages with additional functions in Firefox ?

I have many favorite web pages which I visit very often. But not all of them give me the features and functions I expect from them to be perfectly user-friendly. For example: a button in order to download videos from YouTube, the possibility to search Usenet file names from Forums directly in the NZB Index, etc. I would like to make and add my own customizations, but also find some new ideas from an existing community.
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