This has been driving me crazy for weeks. As Firefox puts the screws on Plugins and Addons (tell me what's the difference?)
It seems Flash video or video that depends on a Flash plugin is getting crazier and more unreliable.
Then FF 26 came out and it got orders of magnitude worse, other Plugins and Addons started freaking out.
Well here's the probable solution;
See there is more than one [Activation, Allow, Block] control in Firefox, yep they figured just one wasn't enough. Worse its hidden and kind of hard to get to.
We all know about Tools>Addons
Or (ok, so what's a Plugin, Addon, or Extension? AlphaBabel Soup please?)
We know about About:config
And we know about About:plugins
But "Did You Know" about [Per-Site/Per-Page] Plugin "Permissions" ???
Everything can be setup perfect, latest version of Firefox installed, latest version of Flash and Shockwave plugin installed, fully up to date and fully patched, fully activated in all the traditional pages.
But if the "Permissions" for that plugin are set to "Block" for that Site/page here is what you'll see:
No clue that the problem is not the new nebulous Firefox overlord "we know best" imbedded defaults (you can't change), no clue it is not the Firefox browser global defaults (you can change), not the Adobe Plugin (actually crashing), that its a "Permissions!!!" problem set on the page by the browser.
Try threading "that Needle Sherlock!"
Now how do you get to that page?
While you browser is Crashing and Flickering you have to
[Right-Click > View Page Info > Permissions]
Survey all of your Plugins on the "chance" that this is the problem, when it could be many others.
[Oh and Firefox is helpfully "bouncing" back and forth from the Crashing Window with the Flash plugin and the View Page Info window.. can you say Seizure? ]
How a Permission gets set like that is beyond me, but I suspect its one of the new defaults in that Blog entry that looks like a EULA that pops up everytime a long running script is slowing down Firefox and it offers to [Stop |or| Continue].
And to make matters worse; this persists both Updating Firefox and Downgrading Firefox, and even if you clear your browser cache and clear your cookies per site and all cookies.
And it appears to "propagate or inherit" if you hit a page with the "Block" permission for a plugin and then link from there to other pages with no custom permission settings sheet.. so if you go through a portal, its really bad.
To be sort of fair; the message seems to be generated by Adobe Flash, but how do they know what Blocked them? A Browser defaults block, a custom property triggered on foul language, a tear sheet with an additional ACL of Permissions per page or element? And that would mean without Adobe's message you would have "no clue" the video was even failing, or missing.
And this applies to [All Plugins]..
Seriously deficient in the common sense communications department.
Do we really need NTFS style per file/page Permissions to Protect "Us" from other peoples webpages? What is it a Filesystem?