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If ytimg.com is blocked by NoScript, I can only view the title, some comments, etc. The show more button usually does not work.
But when I (temporarily) allow ytimg.com it allows show more, but also starts downloading the video ("Aah! It is EATING my bandwidth!!! Stop, disconnect!").
How to view the "show more" info (where useful information or links are provided) without consuming too much traffic?
ytimg.com is where YouTube stores all its static content. (Javascript, stylesheets, etc.) That includes both the script which sets up the player and the script which powers "show more". (They do that to save bandwidth and make things snappier by preventing your browser from sending your YouTube cookies when retrieving files that don't care anyway.)
If you want to have scripts like "show more" without starting the video downloading and you're using NoScript, the simplest solution is to go into NoScript Options > Embeddings and check "Apply these restrictions to whitelisted sites too".
That'll get you FlashBlock-like behaviour (which is designed to be a secure protection against Flash exploits, unlike FlashBlock which is for annoyance-reduction) even on sites which you've marked as trusted.
The only downside is that NoScript for non-mobile Firefox doesn't yet have the extended settings support to allow you to set or unset "Apply these restrictions to whitelisted sites too" on a per-site basis, so you'll get FlashBlock-like behaviour everywhere and you can't whitelist any sites.
The alternative would be to allow ytimg.com and then install Greasemonkey and a script like YousableTubeFix which lets you set "Prevent both autoplay and autobuffering".
