The red font is definitely a stylistic compromise, but I have managed to fix the unreadable taskbar. I've got the instructions in the theme description, but I'll paste them here as well.

Be careful while doing it though, because the menu you have to access can mess up the browser a lot

1: Type " about:config " in the URL bar

2: Type: " browser.urlbar.formatting.enabled " in the provided search box

3: Click the Plus Button on the option

4: Click the switch button to set the setting to false