Bitmap brush tool appears behind sprites in Paint Editor on Firefox

[BryceLTaylor]

Expected Behavior

If you convert a sprite to bitmap and draw over them with the brush tool the line should appear on top of the sprite in the paint editor and on the stage.

Actual Behavior

The line appears behind the sprite in the paint editor, but appears correctly in front on the stage. If you switch to another costume and then back to the one with the line it appears correctly on top of the sprite.

This happens with any of the sprites from the library or a sprite you paint.

Steps to Reproduce

In firefox create a new project
Switch to the costumes tab
Click "Convert to Bitmap"
Draw a line across the cat
Note that the line appears behind the cat in the paint editor and in front of the cat on the stage.

Operating System and Browser

Mac OS 10.13.4
Firefox 59.0.2 (64-bit)