Installing HTTPS Everywhere + security.mixed_content.block_active_content breaks Youtube.com

Issue: With "HTTPS Everywhere" installed and the Firefox setting "security.mixed_content.block_active_content" set to "true" all Flash videos on Youtube.com give the error "An error occurred. Please Try Again Later." This error persists ever after the "HTTPS Everywhere" extension is disabled, removed and/or all options effecting Youtube.com are disabled.

Steps to Reproduce:

1. Create a new Firefox profile and start Firefox.
2. Go to about:config and set "security.mixed_content.block_active_content" to "true".
3. Install the "HTTPS Everywhere" (stable) extension.
4. Visit Youtube.com and try to watch a video.

Expected Results: Youtube video plays.

Actual Results: All Flash-based videos return, "An error occurred. Please Try Again Later."

Tested Environment: Windows 7 (x64) Mozilla Firefox 20

Other: Per Mozilla bug https://bugzilla.mozilla.org/show_bug.cgi?id=834836 , the option "security.mixed_content.block_active_content" will default to "true" as of Firefox 23.

Trac:
Username: pjpii