Spoiler Slayer by Brett Profitt

Spoiler Slayer is an open source, tracking-free, simple extension for Firefox that blocks TV and movies spoilers on your favorite sites. Subscribe in one click to public spoilers lists that always stay fresh and make sure no spoilers slip by, or use the advanced settings to fine tune which spoilers to block on what sites.

Other features include:

• Imports, exports, and subscriptions - Create your list of spoilers or sites and share it with the world!
• Spoiler blur intensity - Blur spoilers to oblivion, or keep them just under legible
• Reveal on hover or click - Feeling brave? Spoiler Slayer can reveal the spoiler when you hover over or click on the censored area
• RegEx support - Anticipate common misspellings of spoilers or only block certain URLs
• Selector helper - It's easy to add new sites with the built-in selector helper, which highlights items on the page as you type
• Blocked counts - Know how many times you've avoided mild panic!

No data is sent to any 3rd party servers by this extension.

Permissions:

• "Access your data for all websites" - Needed to be able to match which sites to block spoilers
• "Download files and read and modify the browser’s download history" - Needed to export and import settings to files
• "Access browser tabs" - Needed to display counts and subscription status in Spoiler Slayer badge icon