Don Johnston Tools/Extensions interact with the webpage/tab you are using them on. Without having access the Extension/Don Johnston tool will not appear on the webpage/tab.

Examples of the "This can read and change the site data settings":

When you click on the extension:

You will need to click on the extenion icon. Chrome will then ask to reload the webpage/tab so the extension can see the webpage/tab.  

(If you have this setting set for multiple extensions, Chrome will have to reload the page for each extension. )

On Current website:

You will have to allow each extension access to each individual website/page you visit for the first time with the extension.

(Chrome will also ask to reload the webpage/ tab at this time to give the extension access to it.)

On all sites: 

The extension/tool will work like it normaly does.

*Recomended setting for Don Johnston tools is having  '"This can read and change the site data" set to: On all sites 

Steps on how to set this setting can be found at:

http://help.donjohnston.net/en/articles/3133784-how-to-set-this-can-read-and-change-the-site-data-to-on-all-sites-for-a-chrome-extension

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