Prevent website from blocking bookmarklet script

Is there a way to prevent a site from doing this blocking via settings, or additional plugins?

Per an answer to this Stack Overflow question, it is possible to disable Content Security Policy browser-wide in Firefox by setting about:config → security.csp.enable to false:

This setting was confirmed to still be available as of Firefox 89.0.1 (June 2021).

As that answer notes, however, this is exceptionally dangerous for general web browsing.

Other options could (possibly) include:

• Filtering incoming response headers via an HTTP proxy (as an incoming response header from the server is how the browser knows to follow a given policy).

• Using some plugin or extension (as you suggest), though there seems to be debate on whether or not this would actually work.

• Running your script as a TamperMonkey/GreaseMonkey userscript as suggested in response to this Super User question.