Is there a way to change the plus icon to an image?

Is there a way to change the plus icon to an image?

Good question. The wrapper simply sets the value of the icon attribute:

<paper-fab-speed-dial-action icon="icons:content-copy">
	Copy
</paper-fab-speed-dial-action>

As I can see, there is no support for a image URL value. And it has no special image tag. You can test it by your own in this live edit example:
[webcomponents.org/paper-fab-speed-dial]
(https://www.webcomponents.org/element/Collaborne/paper-fab-speed-dial)

If you need it, you can submit a feature request on the GitHub page of the original web component:
[github.com/paper-fab-speed-dial]
(https://github.com/Collaborne/paper-fab-speed-dial)

I got a solution. I’m using only java and vaadin, no HTML, and I’ve come up with this:

SpeedDial sp = new SpeedDial();
sp.getElement().removeAttribute("id");
sp.getElement().setAttribute("icon","vaadin:user");

and it works just fine! Now I’m trying to change the background color of it with java :D

OK, you simply want to set an icon to the main menu. I added the icon setter for the SpeedDial in the 1.1.3 release!