Extension does not disappear after being disabled in the Firefox settings

[Nakonana]

After disabling the extension in about:addons (Firefox 82.0.3) the extension is seemingly gone, however if one scrolls down to the bottom of the website, there's a group button in the left corner. If clicked, the guild list expands and you can scroll down beyond the website footer. One can even open guilds...? (but it looks like it's necessary to open the Tavern first...? and it's necessary to wait a little for it to load. Edit: it looks like one has to open the guild at the top first and then work oneself down the guild list one after another to open other guilds)

And if scrolling past the guild list, there's the chat from the guild. It's even possible to Like posts.

At the very bottom of the page is a textbox for sending messages <.< And they go through...

Edit: Clicking on profiles will direct to the profile of the user.

Deactivated all my Habitica related extensions and styles and was still able to reproduce the issue. The chat extension disappears after reloading the tab.

Edit2: updated to Firefox 83.0 - the issue persists

[CraigInches]

Based on the way the plugin works, I am not sure there is a way to fix this issue. Essentially it is actively modifying the webpage in your browser, and when its uninstalled your just removing the scripts that do the modifications. The modifications them selves will persist until you refresh.