My computer has been synching the speeddials for a relaly long time

Even though it is syncing, could you please if all dials already on you computer. If they are there, problem with syncing (visual part) will be fixed next update.

Thank you

Sorry but I don't understand your answer. ...this part "could you please if all dials already on you computer."

Also, since it doesn't seem to be able to complete its synching, I don't know if I can get the dials transferred to another computer. Can I, if it synchs properly?

Wait for our next update, it will be released and fixed soon. Also, the other option is

We got many error reports, rolled back to the previous version. Just reinstall the extension.
https://addons.mozilla.org/en-US/firefox/addon/fvd-speed-dial/

Once we finish fixing major problems, we will launch a new update.  

Unfortunately, you can't keep older version for a long because new FF57+ will automatically disable it. There is nothing we can do, that's how Firefox team implemented. 
We try to fix everything that is possible.

Also backup your profile folder:
https://www.google.com/search?q=how+to+find+firefox+profile+folder&rlz=1C1CHFX_enUS749US749&oq=how+to+find+&aqs=chrome.0.69i59j69i57j0l4.3135j0j1&sourceid=chrome&ie=UTF-8

Thank you.