I am running Firefox 39.0 in Debian Unstable and KDE.

I have installed the latest flash player plugin. Mostly it works but on some sites the space where there will obviously a flash animation, or a Youtube link, is blank.

I have tried various "fixes" I found on the web but none has fixed this problem. I don't get a warning and an "allow" button. Either a blank space or a "you need an update" message.

Any help will be appreciated.

You can got into about:config and set it to use flash as default other wise it is always default to html5 first. I would make sure libx264 is installed it helps. But the truth is html5 has been on it's way in for 10 years now and is going to be taking over the internet.
There is a cookie for that page ? maybe that is blocking it. etc.
here some good reading. http://kb.mozillazine.org/Extensions.blocklist.enabled

Which version of Flash of you have installed? I believe the latest is 11.2.202.491.
I have only seen this issue when I run an outdated version of Flash.

I just use the flashplayer-mozilla package. It works fine with Firefox Nightly (ver. 42.0a1)
jdk

I use nightly also. What I meant was have you checked whether you're running the latest Flash with the following?AS far as I can tell Debian doesn't update Flash automatically so update-flahsplugin-nonfree has to be run periodically to keep Flash up to date.

seeing as adobe STOPPED supporting Apple and Linux
the linux version of flash is 11
the Windows is 18

and a lot of sites are USING the adobe flash 18 DRM that IS NOT supported in flash 11


use Google chrome

or use MS windows

but Chromium seams to work on most sites

That may be substantially true, however, Adobe does provide security and bug fixes for Flash 11 on Linux (I installed a new version the other day) and Mozilla have Firefox show the warning when the latest Linux version is not installed. Apart from the problems with DRM (which I am not convinced could not be resolved by installing HAL if I took the time) I have had no problems with Flash on Linux in day-to-day use.
Of course I, like many others, will be happy to see Flash die a death but until it does I will continue to keep it as up to date as possible.

i would put it at about 2/3 of the sites i use that have flash DO NOT work in firefox
but do in Chromium

there are SO MANY that DO NOT work in firefox that about 1/2 of the bookmarks are now in Chromium

Of course not. Why would I do that? As I said above I use the flashplayer-mozilla package and I am running the latest version. When I installed the latest version (some time ago) the warning messages disappeared. I don't use the flashplugin-nonfree. It doesn't work for me. In general since I run Debian Testing, I update my system every day.
Debian certainly updates the flashplayer-mozilla automatically like any other package.
does the trick.
jdk

Ah, my apologies, I hadn't noticed there's flashplayer-mozilla in deb-multimedia. I might have to give that a go some time and see whether it works better.

No worries. Let us know how you make out.
jdk