A. Tor browser can and almost certainly will leave recoverable traces on your drive, if you don't encrypt SWAP this is even more likely to happen B. FDE can save the day and has many times.... C. If the person after you knows or suspects you are using FDE they will with high probability be able to get around it, there are plenty of cases of LE carrying out cold boot attacks and using other passphrase stealing tactics against targets they know to be using FDE. It really boils down to yes of course use FDE, but also be aware that is is a very limited technology. IMO FDEs primary threat model is to keep your information safe if a thief steals your corporate laptop, it is not really meant by itself to keep you safe if some highly trained LE forensics people are after you. However, if some unskilled LE agency is after you it could very well save your ass because they just shut down computers and send them off to the lab, they don't have forensics specialists on site for every raid. They don't have enough computer forensics specialists to send one to every raid and their average door kicker agent isn't going to be trained to properly deal with FDE. Pwning a target with FDE requires serious tactical planning and computer forensic / technical knowledge (at least enough to install a key logger, at most enough to analyze transient electromagnetic information leakage), not everyone who gets raided has these sort of resources aimed against them, but if you do chances are high your FDE will be bypassed unless you take exceptional counter measures.