Glad you asked well here I will list the levels:

[Walk in the park]

[Bridge on the river TY]

These levels have the fireflies.
{NOTE: that you can get the baskets once unless exiting and coming back into the level.

Walk in the park has them right behind you when you spawn in the level.
Bridge on the river TY is at the very end of the level when you get to the cheapscape's house they shoud be there.

To get the baskets you must aim at the fireflie when hit they become dark and fall but there is a small chance of one to spawn so keep trying till you get one.

Once you do, you could get an extra life, magnet, or heath these items are usefull when low on heath and trying to find that last opel, so good luck and have fun!

Getting a basket






Missing anything or improvement let me know in the comments!