Am playing in a game with some friends. Recently swapped over to Firefox from chrome, and I noticed an error with the sheet

The circles there at the top are supposed to be buttons for different tabs on the sheet labled Character, Skills & Spells, Combat, Gear & Notes, and NPC Sheet. They're supposed to have the name of the tab there, but as you can see they don't display that. it was working fine in Chrome. Anyone know what's up?