Install the extension.

Pokkén Tier List Maker

The extension icon should appear in your Chrome menu.

Next

Go to the Tier List Maker

Tier List Maker

Change the game and you're ready to go.

Install the add-on.

Pokkén Tier List Maker

The add-on icon should appear in your Firefox toolbar.

Next

Go to the Tier List Maker

Tier List Maker

Change the game and you're ready to go.

Install the Chrome extension installer.

Install Chrome Extensions
Next

Install the extension through the Chrome Web Store.

Pokkén Tier List Maker
Next

Go to the Tier List Maker

Tier List Maker

Change the game and you're ready to go.

Using Firefox mobile

The Firefox app allows you to install add-ons, and this tier list maker works on the app! Just come back here on the Firefox app and use the normal Firefox instructions.
Otherwise, you can try (this seriously almost never works)...

Bookmark this link:

Tier List Extension
Next

Go to the Tier List Maker

Tier List Maker

When you are on the Tier List Maker page, click the link you have bookmarked to run the extension. You must click the bookmark each time you visit or refresh the Tier List Maker page.