Counter Readability in Dark Mode

[Riajyuu]

Firefox has built-in dark theme. When users set normal or light theme, dark counter is still good. But it is completely unreadable when user sets to dark one. The solution is to add listener to theme changing. When users set the dark one, change text to white. If you don't know how, this can help: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/theme/onUpdated

[Loirooriol]

I have been thinking about this. The problem is that theme.onUpdated is rather useless, because it's only fired when calling theme.update() or similar, but not when the user changes the theme.

The way to define different browserAction icons depending on the theme is theme_icons in the manifest, but can't be set programmatically. See https://bugzilla.mozilla.org/show_bug.cgi?id=1484840