The Firefox plugin updates the Zotero icon in the toolbar according to the page content/document type it can save in Zotero.

However, I find this behaviour disturbing, as it makes it harder to identify the toolbar button.

I'd like a setting in the plugin preferences that would allow the disabling of this behaviour, so the 'Z' icon would be consistently displayed instead.

I'll see if I can make a pull request to that effect.