Hi I found a small bug (one of those bugs hard to track) on the third Esperanto lesson about colors (LESSON 3 - esperantajn, flavajn, rozo, rozkoloraj, oranĝkolore, violkoloraj, floroj).
One of the tasks is to translate "The book is orange, purple, and yellow." to Esperanto.
The bug is: When i pass the mouse over the word "yellow" to see the translation in Esperanto (which is "flavo") the tool tip appears but the word yellow that is the first word of the second line before i pass the mouse moves to the end of the first line. e.g.:
Before i pass the mouse: The book is orange, purple, and yellow.
After i pass the mouse: The book is orange, purple and yellow .
The main issue is that when the word moves the tool tip disappears, and when the tool tip disappears the word "yellow" moves back to the second line making the tool tip appear again; The result is blinking tool tip that i can barely read.
I tested this bug on Firefox (38.0.1) under Linux. I tried to replicate it on chrome on Linux, chrome on Windows and Firefox on Windows with no result, the bug only appear on Firefox on Linux.
I took two screenshots showing the bug:
I hope it helps.