Thunderbird launches a browser when image URL's are in the message

[Douglas Phillipson]

I'm not sure when this started happening but Thunderbird started 
automatically launching a Firefox "Tab" for every URL to an image 
embedded in an html email.  If I read an email with many URL's to images 
I get tons of tabs with the those darn tiny  images, one tab per image.  
I don't see a configuration option in  Thunderbird's  "about:config" to 
turn this off.  Am I missing the obvious?

Thanks

Doug P