Related discussion:
uBlockOrigin/uAssets#7636 (comment)

Related issue:
uBlockOrigin/uBlock-issues#2844

Related issue:
uBlockOrigin/uBlock-issues#2828

Prevent usage of specific or all (default) canvas APIs.

Syntax

```text
example.com##+js(prevent-canvas [, contextType])
```

- `contextType`: A specific type of canvas API to prevent (default to all
  APIs). Can be a string or regex which will be matched against the type
  used in getContext() call. Prepend with `!` to test for no-match.

Examples

1. Prevent `example.com` from accessing all canvas APIs

```adblock
example.com##+js(prevent-canvas)
```

2. Prevent access to any flavor of WebGL API, everywhere

```adblock
*##+js(prevent-canvas, /webgl/)
```

3. Prevent `example.com` from accessing any flavor of canvas API except `2d`

```adblock
example.com##+js(prevent-canvas, !2d)
```

References

https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/getContext

Related issue:
uBlockOrigin/uAssets#19903

This is done by taking advantage through Firefox-specific
contentScripts.register() API:

https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/contentScripts