Finding Fifi - Full Walkthrough (SPOILERS)

This guide represents a full walkthrough of the game. Please keep in mind that it is SPOILER-HEAVY!!!
For a list of hints with less spoilers, please check the official guide written by the devs.

Full walkthrough

Fireplace:
🃏 Card #1: on the chair, under the pillow.
Mirror: pick up the yellow button.
Plant pots: pick up the key.

Christmas tree, snowman shelf:
🃏 Card #2: on the right side of the shelf
Pick up the candle from the left side of the snowmen shelf.

Christmas tree, left side:
Click on the box with a yellow bow and pick up the fishbones.
Pick up the black cat statue (red collar) in front of the tree.

Locked cabinets:
Pick up the snow globe (left side).
Place the candle on the right side, in the green candle holder with 3 slots.
Optional: If you place the snow globe in one of the other slots (inspect it first to press the button on it and turn off the snow), you'll see that it projects a certain number on the wall depending on what item you have selected inside the snow globe.

Door:
🃏 Card #3: in front of the door

Bookshelves area, piano:
Pick up the black cat statue (green collar) sitting on the piano.

Bookshelves area, left bottom shelf:
Pick up the bone.

Bookshelves area, middle shelf:
Pick up the black cat statue (yellow collar).

Bookshelves area, click on the snowman to zoom in:
Pick up the book. You can open it by inspecting it and then using the key you picked up earlier from the plant pots next to the fireplace.

Bookshelves area, between the bookshelves and the piano:
🃏 Card #4: feed the fishbone to the yellow cat sitting in the red box.

Fireplace:
Place the 3 black cats. Optional: clicking on each of them will give you hints on how to unlock some of the cabinets.

Christmas tree, left side:
Place the button on the Buddha painting and press it for a clue: middle, right, middle, right, left.

Snowmen puzzle:
Press them in the following order (hint given by the sounds emitted when you click on the green collar cat from the fireplace):
Snowman shelf: left snowman
Bookshelf, left side: snowman hanging on the plant pot
Snowman shelf: right snowman
Snowman shelf: left snowman
Bookshelf, right side: snowman hanging on the Morse code panels
🃏 Card #5: on the Christmas tree

Locked cabinets:
Open the left most cabinet using the code 27357 (hint given by the last page of the book (the only one that has 5 elements) combined with the snow globe projections in order to find out the correct digits: tree = 2, star = 7, Santa = 3, reindeer = 5, stars = 7); this gives you a clue for Card #9.
🃏 Card #6: open the second cabinet from the left by setting the handle to the following positions and pressing the button next to it after each move: middle, right, left, middle, left (hint from the Buddha painting puzzle: 12345 = middle, right, middle, right, left combined with the eye symbol clue next to the door 12.5.15 => middle, right, left, middle, left)
🃏 Card #7: inside the second cabinet from the right, open it using code 88
🃏 Card #8: inside the right-most cabinet, open it using the following combination: full counter-clockwise, semi clockwise, semi counter (hint given by the footprints displayed in front of the fireplace when you click on the red collar cat)

🃏 Card #9: after opening the left most cabinet using code 27357, click on the following cats based on the clue uncovered: black cat from the bookshelves left side ('Book'), white cat from the Christmas tree ('Mystery'), black cat sleeping in the basket from the bookshelves right side ('Dream').

Inspect the 9 cards you collected and solve the jigsaw puzzle.
When you're done assembling the picture, drag the bone in your inventory on the bone slot below the tree from the picture and click on it to finish the game.