'Error loading plugin: Plugin file not found' message on ONLY 5 sites, but all others OK. Help, please!

Hi Again!

I posted this problem here before, but since I really need to access the sites that receive this error message in less than a month, I had to re-post; hopefully someone who didn't see it before will see it & have a solution for me.

Here are the details:  I'm running windows 8.1 & I use Firefox 33.1.1, Pale Moon 25.1.0 or Opera 26.0 as my browsers, (I have IE installed & up-to-date, but I never use it).  I followed the 10-point checklist on Adobe & everything was done, except for "uncheck Hardware Acceleration" in Flash 'Settings'; I tried to uncheck it on this site, where it's indicated, as well as in my 4 browsers when I'm doing something that uses Flash, but no matter how hard I try, I can't 'uncheck' the check mark in that tiny box!  Since this error problem only affects 5 web sites, & I can watch streaming media on all other sites, I don't think it's an issue. 

Here's how this problem began:  I was watching a live, streaming nest-cam on 5/09/14 around 11:00AM, (yes, I DO know the exact time & date, because it happened so suddenly while I was watching this website that I'd been watching since the end of February, 2014), when my screen went black.  I thought it was probably an Adobe Crash, but when the usual Crash Report window didn't show up, I just closed Firefox & reopened it, expecting to resume watching the nest-cam.  When I went back to the site, I got the black screen with the "Error loading plugin: Plugin file not found" message.  The chat portion on the site still works, though. I know there are other sites with this nest-cam feed, so I started trying them, but it took several tries for me to find one that didn't get the error message! I posted this problem on "Windows BBS" forum, & someone else posted that the same thing happened to them AND on the same sites!  They didn't have a solution, either.  I cleared my cache, rebooted my PC & even did a System Restore, but whatever happened in that brief second made using ONLY 5 sites impossible.  Here are the sites that receive the error message:

http://pixcontroller.com/eagles, (but I CAN go to http://pixcontroller.com, but there isn't any streaming media)

http://cbslocal.com/eagles

http://westmorelandconservancy.org/BlueBirdwebcam-1.htm

http://wildearth.tv/cam/pittsburgh-bald-eagles, (I get the error message on ALL cams on this site)

http://aviary.org/BE-NestCam1 (I get the error message on ALL cams on this site)

Now if any videos from the 5 websites above are uploaded to YouTube, I can watch them perfectly...no error message if I watch the videos elsewhere.  Luckily, I found Ustream, & they have most of the nest cams I watch, but I need to fix this issue, because it's nearing nesting time!  I'm an amateur nest-watcher & it's vital that I have access to these 5 sites, so if anyone knows how to fix this, PLEASE tell me!

Thanks for taking the time to read my post.

All suggestions/solutions are gratefully accepted.

Thanks in advance for your help!

DogPal