So, it's not only youtube site, it's other sites, just heavy ones. Assumingly, youtube page, without the flash (blocked).

I'm not sure flashblocker blocks flash, I think it blocks the site flash, meaning it replaces the site flash with one of its own (we bay be talking about another addon?).

I'm not sure if you can find a heavy site that doesn't have flash. Darn thing is omnipresent nowadays.

Do the same sites work fine in Firefox 4 for N900? Or Opera.

Also, there's something I'm missing here. You said you flashed it, so I understand that clean-flashed-completely-naked N900 still does that for you? Because it doesn't for usa and we all have the same software (Assuming you flashed PR1.3 0 - did you?).

Or did you reflash, restore and then try?