Is it illegal to sell or use fb.something domain name?

I'm not 100% certain about this one but from what I understand.... as long as the content on this site is not a direct refference to Facebook then you should be okay...I mean FB could be an abbreviation for your site called FunnyBunny or something like that

deez007 said:

I'm not 100% certain about this one but from what I understand.... as long as the content on this site is not a direct refference to Facebook then you should be okay...I mean FB could be an abbreviation for your site called FunnyBunny or something like that

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Thank you. Is there any legal rights for them, if I use it for other purposes without using any facebook brand properties?

FB does not necessarily stand for facebook. Now it depends on usage. It's just an ordinary LL.
HP is an LL too, but it gets tricky here because Hewlett Packard is usually known as HP. Facebook is not commonly known as FB yet (AFAIK).
The bottom line is, don't buy domains without a good reason, especially to sell it to a TM holder.

I agree with deez007
It's fine to sell

Even if it was a trademark it could still be sold hence exhibit a :

Facebook.to recently sold for $719

http://domainnamessold.com/domain-names-sold-recently/domain-names-sold-recently-august-19th-2016/