Hi, just some information: I am not associated with FVD and or Nimbus addons - am just another user. 

I also struggled for the past few weeks and the end result is:

after testing and manipulating with the FVD speeddial in firefox, I tried also waterfox - to no avail. Nothing worked and it got so bad that it was handicapping my work.

I went on the search, and many years ago [around 2002 or so] I had used opera, but abandoned it when firefox came out.

Now: my findings are as follows:

FVD speeddial is just one of the many developers that fell victim to a far premature firefox release, that is unable to cope with allowing legacy to still run paralell. It does not work.

I was in constant contact with the FVD dauthor, and we were trying everything to fix and at least get it to work halfways.

Yesterday, I finally gave up after countless hours wasted since November 14th. Though, it always looked like as if it was just "FVD" that was the problem, while Firefox zoomed right by with its so very reduced "speedy" shiny new toy. It was Firefox all along, them scrambling to try to ride 2 horses at the same time.

I installed Opera, installed FVD Speeddial, as well as all other extension that Nimbus offers, installed also some of the most important extension opera has to offer and voila=

the result is: there is nothing wrong with FVD or any other extention of theirs. It is FIREFOX that has to be blamed in it entirety.

After weeks of being totally handicapped by this firefox disaster - I now am back to work with speed, all the extension that no longer worked in FF, but work just fine in Opera.

I had also installed firefox 57, just to see - and my results are:

OPERA  is actually faster than the new firefox, measured that by having far more extensions installed now in Opera, where as in firefox it was limited to the useless few that actually somewhat resembled what we had before in FF - and opera won out even on heavy websites by at least 7 to 11 second faster.

I will never return, am now a happy camper, prefer at this point Opera over all others [like vivaldi etc] and will stay with it.

I am around a long time, since 1993, that makes me older than any other browser, when there was only IE and netscape [wars were on the daily order], so, yes, I can give some insights throughout the years what is now a must have for developers, website designer etc. - and with close to 3000 dials at this point, I would have been devastated without FVD.

THANK YOU FVD developers for not only the Speeddial but also all your other extensions you offer. For any harsh words of anyone in here, I would like to apologize for those that do nothing but complain, some with uncalled harsh critic. No one complained when everything was going OK, no one ever gave a second of a thought, that the developers of this extension provided this one for free all these years. Now, that there came a hurdle to jump, many are awfully quick to criticise. 

The author deserves better than that. Shame on you, being rude and without consideration of what it takes to not only create, develop a massive extension as FVD Speed Dial is, and maintain, constantly update it throughout the years without ever charging a penny for all the work hours they put in over the years - Instead of being grateful that you were able to use it in the first place.

It just makes me angry when I read rude remarks toward someone that has only been giving and providing a service for free for years.

People can be better than that - all it takes is a simple Thank you, and a polite question to the author. Keeping in mind that they too have to earn a living. They surely are not earning it with FVD.