Stun, Daze and similar stuff don't impede your movement...
...they make your mind funny.
While you are stunned, there's nothing holding your body to move. You just can't think right to actually do something. If you take a really hard blow to your head, that won't make your body harder to move - it will make your brain go gonzo for a few secs, before you became aware of what's really happening.
Stun is not about movement, is about senses of what's going on.
Freedom of Movement makes "your body work right", not anything else. It allows you to move, but not allows you to think. You can't think if you're dead. Or Stunned.
Paralysis don't block purely mental actions, so it don't block "thinking".
Slow makes your body... well, slower, but it doesn't affect your thinking.
Web is... well, a web. It hinders your body, not your mind.
Stun, Daze, Dazzle and similar stuff, on the other hand, makes your senses go wacko, so they aren't really blocking your movement. Stun never stopped you from moving, it just stopped you from thinking for a while - and since you don't think, you don't act.
So, the point is,
If something affect your senses, Freedom of Movement can't help you.
Think like a "Houdini Effect". Houdini can escape from almost anything, considering that he
knows what's going on. If you throw him with a concussion inside a closed coffin... well... he will stay there.
So, to determine what Freedom of Movement removes or not, use a simple rule:
Why I can't move?
If you can't move because a spell or something is hindering your body to move, like Web, Freedom of Movement can help you.
If you can't move because a spell or something is making your brain go gonzo, like Stun, or because your body becomes something that can't normally move, like stone from Flesh to Stone*, it won't help you.
*Flesh to Stone don't impede your movement, it merely limits you to the movement that a stone statue is allowed to do. A "Freedom of Movement"-ed and "Web"-ed person would become a completely untangled stone statue.
Also, read Freedom, the 9th level spell:
The subject is freed from spells and effects that restrict its movement, including binding, entangle, grappling, imprisonment, maze, paralysis, petrification, pinning, sleep, slow, stunning, temporal stasis, and web. To free a creature from imprisonment or maze, you must know its name and background, and you must cast this spell at the spot where it was entombed or banished into the maze.
Emphasis mine.
Freedom removes a bunch of effects, like Flesh to Stone and Stun. It would seem rather... strange to say that a way lower-level spell can do almost all the things that a 9th level spell can. Freedom is Freedom, not Freedom of Movement.
A creature usually can't take a 5-foot step to enter a square that hampers the creature's movement
When determining the movement costs for hampered movement, the game usually doesn't care where the creature is and instead cares where the creature's going:
Difficult terrain, obstacles, and poor visibility can hamper movement (see Table: Hampered Movement for details). When movement is hampered, each square moved into usually counts as two squares, effectively reducing the distance that a character can cover in a move.
If more than one hampering condition applies, multiply all additional costs that apply. This is a specific exception to the normal rule for doubling.
In some situations, your movement may be so hampered that you don't have sufficient speed even to move 5 feet (1 square). In such a case, you may use a full-round action to move 5 feet (1 square) in any direction, even diagonally. Even though this looks like a 5-foot step, it's not, and thus it provokes attacks of opportunity normally. (You can't take advantage of this rule to move through impassable terrain or to move when all movement is prohibited to you.)
You can't run or charge through any square that would hamper your movement.
Emphasis—and extra emphasis—mine. Thus at issue is the creature's destination square not its current square. The creature's already in its current square, so the creature doesn't have to care about that square's terrain, having already overcome the difficulty of entering it!
For example, going from a square of supernatural darkness into an adjacent square of bright light is just normal movement, but going from a square of bright light into an adjacent square of supernatural darkness usually costs double movement due to poor visibility. In fact, going from any square into an adjacent square of supernatural darkness usually costs double movement due to poor visibility, the condition of the starting square typically not mattering at all.
Exiting then reentering the same square of hampering terrain still costs additional movement, of course. A creature can't move normally back and forth between squares of hampering terrain just because it's occupied the same square of hampering terrain previously. For example, moving from a square of supernatural darkness to a square of supernatural darkness then back to the original square of supernatural darkness does not speed up the return trip.
Best Answer
By RAW Freedom of Movement does, Freedom doesn't. Freedom of Movement ignores anything that would impede your normal movement, this includes encumbrance and difficult terrain. Freedom is very specific in what it frees you from however, not to mention Freedom is an instantaneous spell so it only helps you in the immediate. So even in the case of something like web, if you were freed and then immediately failed reflex again and got stuck, you'd have to cast Freedom again. Freedom of movement just wouldn't let you get stuck by anything as long as it's working.
Although you bringing it up in that case you could rule it that the squares of difficult terrain you're currently in turn into normal terrain, and that all your gear falls off. However that wouldn't be RAW, it'd just be funny.