I'm using the most current version of the Firefox plugin on FF 56.02, on Windows 10 1803.

Clicking "save to zotero" occasionally opens a new tab, where you can select from 1 or more references to save.

However, clicking "OK" in the bottom right of the tab, or the "x" (close) command on the tab forcibly terminates the browser. This happens regardless of whether you select any of the references or not.

The address bar in the browser starts with moz-extension://

I have Tab mix plus 0.5.04 installed, with [options]Links > "Open links that open a new window" set to "open in a new tab".

This has happened with Springer publishing books that list multiple chapters on the same page

Here's an example:

1. Go to https://link.springer.com/book/10.1007/978-3-319-64177-5
2. Note that the Zotero icon is a folder (link contains multiple references)
3. Click the Zotero icon.
4. (for me) A new tab appears, listing all the references (chapters in the book).
5. Selecting one, then clicking OK, closes the browser. The reference is NOT added to Zotero.

In a fresh install of FF, with tab mix plus disabled, the window that appears (listing the references) appears off-screen somehow. I can see it in the previews that appear in the taskbar, but I can't select the window and have it appear on-screen.

Behaviour in Chrome 68 appears normal: the window appears with the references, and selecting one and clicking OK adds it to Zotero correctly.