Please check if all your plugins are up-to-date. To do this, go to the Mozilla Plugin Check site.

Once you're there, the site will check if all your plugins have the latest versions. If you see plugins in the list that have a yellow Update button or a red Update now button, please update these immediately.

To do so, please click each red or yellow button. Then you should see a site that allows you to download the latest version. Double-click the downloaded file to start the installation and follow the steps mentioned in the installation procedure.

My only plugins (both up-to-date) are:

1. Adobe PDF Plug-In For Firefox and Netscape 10.1.4
2. Java Deployment Toolkit 7.0.90.5

nothing that disables playing videos as I open web pages. I have a limited monthly broadband allowance and I hate it being wasted on advert videos while I surf the web. Google chrome lets me disable them by default but would prefer Mozilla.

Are you using any Adblock extension(Addons)

You can enable click-to-play in Firefox, but this feature has not been fully implemented in current Firefox version and may cause some plugins like Java and the Adobe Reader to malfunction. So use this at your own risk

• https://wiki.mozilla.org/Opt-in_activation_for_plugins

You can also look at this extension:

• https://addons.mozilla.org/firefox/addon/stop-youtube-autoplay/

Thank you cor-el, I found it in the about:config page and it works exactly the way I wanted. :o)

Note: I also did try the stop-youtube-autoplay but apparently a fix will be necessary due to use of html5 on youtube now. Opting out of the youtube html5 trial did not seem to help.

For HTML5 there there may be this pref to prevent auto start: media.autoplay.enabled