Could you check whether the Shockwave Flash plugin has been switched from "Always Activate" to "Ask to Activate" on the Add-ons page?

Tools menu > Add-ons > in the left column click Plugins

If Firefox won't let you set Shockwave Flash to "Always Activate" this can indicate that the currently installed version has been listed in the block file. However, the current version seldom is blocked...

If the change sticks for the duration of your session, but reverts when you exit and restart Firefox, it could be the user.js file in your profile folder. This article describes how to track down and, if appropriate, delete that file: How to fix preferences that won't save.

Also, you have the Flashblock extension, so if the built-in setting is already correct, please check the settings in Flashblock, or disable it.

You may also want to check the user.js file that your System Details List shows that this file in present in the Firefox profile folder.

You can use this button to go to the currently used Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)

The user.js file is only present if you or other software has created this file and normally it wouldn't be there. You can check its content with a plain text editor (right-click: Open with) if you didn't create this file yourself.

The user.js file is read each time Firefox is started and initializes preferences to the value specified in this file, so preferences set via user.js can only be changed temporarily for the current session.

• http://kb.mozillazine.org/Preferences_not_saved

Uninstall the Flashblock add-on from the Add-ons Manager, Extensions category.

• Disable or remove Add-ons

It was the Flashblock thing.

I forgot I had installed that.

Thanks, all, for your tips.