A clearance is held by a specific agency. Say I work for contractor company C, on a contract with three-letter agency TLA. TLA grants me a clearance at whatever level, and they keep track of it. If I switch jobs to another position that requires a clearance -- maybe I go to company D, maybe I stay at C but on a contract for four-letter agency FLA [1] -- then TLA can transfer the clearance to the new agency FLA, and now FLA is the holder. Depending on the specifics of TLA and FLA, this can be "quick" (in government time), or in the worst cases it will take just as long as getting a clearance from scratch.
If I go to company D, but the new position does not require a clearance, then it becomes inactive. I can say I previously had a clearance, and if not much time has passed then getting it reactivated (if I go to a third job that needs it again) may be a relatively quick process. But if I am not at a job that is keeping it active, then I have no right to access classified data or anything.
In other words, if Facebook is hiring cleared people, they have to be working with a government agency that is holding the clearances.
On the other topic: obviously you have to be a US citizen. Immigrants/naturalized citizens are fine; I've known many cleared immigrants. Dual-citizenship I'm not sure about, you might have to renounce your old citizenship.
A clearance is held by a specific agency. Say I work for contractor company C, on a contract with three-letter agency TLA. TLA grants me a clearance at whatever level, and they keep track of it. If I switch jobs to another position that requires a clearance -- maybe I go to company D, maybe I stay at C but on a contract for four-letter agency FLA [1] -- then TLA can transfer the clearance to the new agency FLA, and now FLA is the holder. Depending on the specifics of TLA and FLA, this can be "quick" (in government time), or in the worst cases it will take just as long as getting a clearance from scratch.
If I go to company D, but the new position does not require a clearance, then it becomes inactive. I can say I previously had a clearance, and if not much time has passed then getting it reactivated (if I go to a third job that needs it again) may be a relatively quick process. But if I am not at a job that is keeping it active, then I have no right to access classified data or anything.
In other words, if Facebook is hiring cleared people, they have to be working with a government agency that is holding the clearances.
On the other topic: obviously you have to be a US citizen. Immigrants/naturalized citizens are fine; I've known many cleared immigrants. Dual-citizenship I'm not sure about, you might have to renounce your old citizenship.
[1] This is an NGA joke. NGA: because the intelligence is silent. https://en.wikipedia.org/wiki/National_Geospatial-Intelligen...