speeddial set as FF homepage, but it doesn't open until I click to open a new tab.

Hello! Try this:

Go to the extension settings and copy the address
http://nimb.ws/H1W7qP

2
Open Firefox Settings
http://nimb.ws/cokXtr

3
Select Home page settings

Replace options.html with newtab.html
http://nimb.ws/CMxYdg

Thanks, that was already set.

The problem is only when opening FF from a closed state, the speeddial tab either takes a long time to load, or doesn't load until I click to open a new tab.

Having the exact same problem, did you find a solution?