What is that plugin for? Have you tried to re-install it?

Thanks for your reply. I made a mistake - it's actually an unresponsive script, rather than a plug-in, but the problems are as described. Hope you can help.

What is the message about the script say? All of it.

Hello,

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Thank you!

With a site name like js.moatads.com I can't help thinking this is for some ads appearing in the page. Not that we don't need to support free content, but perhaps you should block that script from loading if it is broken/dysfunctional. You can use the YesScript extension to block scripts on a site-by-site basis.

https://addons.mozilla.org/firefox/addon/yesscript/

Thanks for your help - I've installed the add on, although strangely the script seems to have stopped misbehaving. All's well that ends well! Thanks again.