There are difficulties with placing Blue Fire in survival mode, most of the time not placing at all.
Occasionally, the fire can be seen, and if placed at your feet, you can obtain the Curse effect, but the fire isn't placed. Rarely, it does place.

I believe this might be the jar both placing and picking up the fire at the same time, due to placement working just fine if the empty jar is used in any open slot except the first, the fact the fire flickers in for a slit second occasionally, and the item in the inventory and first person hand moving in the use animation.

Maybe add a slight delay in the usage like the bucket?

Steps to reproduce:

1. Enter game mode Survival
2. Obtain the Blue Fire Jar
3. Place the jar in the first open hotbar spot
4. Right-click to place fire

Running in:

• Biomes O' Plenty: 7.0.1 (7.0.1.2399)
• Minecraft: 1.12.2
• Forge: Release 14.23.4.2757

I'm having the same issue, it flickers for a sec and then jar is back to normal and no flames.