Conflicts with Flash 11.5.502.146 Rated 4 out of 5 stars
I'm still rating the addon 4 stars, because it's worked so beautifully for years. Sadly I'm having to uninstall it, because it stops YouTube videos from playing. Oddly enough Hulu still plays, and the Flash movie on the "Check your version of Flash" still plays, but YouTube is dead....UNTIL I disable/remove the Pearl Crescent add-on.
I've tested and verified this on 2 different machines, one running XP with Firefox 18; the other running Windows 7 and Firefox 18. Both have the latest (at this writing) versions of Flash installed (11.5.502.146) and the Firefox Shockwave Flash plugin (v11.5 r502).
I know it sounds crazy, but I've spent the past couple of hours testing this. disabled/re-enabled/safe mode/disabled/re-enabled this addon. With it enabled, YouTube videos are all a black box, without it, they start and play fine on 2 different machines.
Another annoyance (to me as a developer, not to the average user, most likely), the CSS errors from Pearl Crescent "bleeds over" when doing an initial error check on another page in another tab using the Web Developer tool bar.