If you haven't already tried this, please disable the Flash player plugin's protected mode feature. The following pages/posts provide different ways to disable that feature:

• Adobe support article under the heading "Last Resort": Adobe Forums: How do I troubleshoot Flash Player's protected mode for Firefox?

• Manual steps: https://support.mozilla.org/questions/968190?page=5#answer-509209

• Batch file to automate the manual steps: https://support.mozilla.org/questions/982093#answer-518078

Flash needs to completely unload from memory (restarting Firefox might help) before this would take effect.

While you are troubleshooting this, it might be helpful, to avoid unnecessary pain on sites where Flash is not actually essential, to set Flash to Click-to-Play ("Ask to Activate"). This will delay Flash from starting on a page until you approve it.

To set "Ask to Activate", open the Add-ons page using either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Plugins. Look for "Shockwave Flash" and change "Always Activate" to "Ask to Activate".

When you visit a site that wants to use the Flash, you should see a notification icon in the address bar and one of the following: a link in a black rectangle in the page or an infobar sliding down between the toolbar area and the page.

Flash might not work any better after you approve it, however...

One more: In case one of your extensions is involved, could you test those two sites in Firefox's Safe Mode? That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. More info: Diagnose Firefox issues using Troubleshoot Mode.

You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

Not all add-ons are disabled: Flash and other plugins still run

After Firefox shuts down, a small dialog should appear. Click "Start in Safe Mode" (not Reset).

Any difference?