On the background options page in settings, do this:

There is a browser add-on that will do it for you. Speed Dial will open as homepage, but tabs can be controlled to open with an option of your choice. Some offer choices of what type of tab page and others simply open a blank tab.

To add, when dials periodically update they appear in a windowed Firefox window when hovered over in the taskbar instead of a maximized window of which Firefox is actually running. Perhaps the reason Firefox new session opens windowed most times.

Well, I have to say either you or Mozilla staff did something to help with the new speeddial update. I had the legacy installed, but got a forced update to the newer version. I have to say the preview resolution is improved from the first version update. The sites are still somewhat overblown in the largest thumbnail size, but it's doable. I had to remove the dial that pointed to a local html file because the window continuously clocked. Once removed, all the previews load. Here's a screen shot of the most recent speeddial update. Money dot com international markets dial replaces the local weather html file.

Unrelated, I would suggest you set the default dial refresh rate to something greater than 1 minute. I know it can be configured, but for some not so tech savvy, something like 15 minutes might be better for the Internet while still providing the ability to reduce time down to 1 minute if desired.

Thanks for the rollback link. I hope your team will be able to work out the bugs and through the Firefox limitations. As a comparison, here is what the legacy version looks like with the same URL thumbnails. Couldn't get the full screen, but there is enough to see the difference.

Also found the Speed Dial new version Intro window will pop occasionally and afterward the thumbnails become overblown and skewed. Doing a Refresh All (which continuously clocks all thumbnails), then quitting and restarting Firefox will put them back the way they were as shown above. BTW, dials 7-9 display when this happens but clocks again after the Refresh All and Firefox restart. Search is disabled in settings and the icon does not appear when this happens.

1. https://finance.google.com/finance
2. http://cnn.com
3. h ttp://images.intellicast.com/WxImages/RadarLoop/pie_None_anim.gif
4. http://whatismyv6.com/
5. https://www.news4jax.com/
6. h ttp://images.intellicast.com/WxImages/RadarLoop/usa_None_anim.gif
7. file:///C:/Users/removed/OneDrive/Weather/WeatherInfo.html
8. http://www.npr.org
9. h ttp://images.intellicast.com/WxImages/SatelliteLoop/hiatlsat_None_anim.gif

Broke http for the GIFs so they wouldn't load here.

Websites are overblown, fuzzy, out of focus.The weather GIFS are not overblown, but they are rendered poorly.

In addition, 7 thru 9 thumbnails continuously clock. 7 is a local html file. 8 is npr.org. 9 is another weather GIF.

Firefox 56.0 (64 bit)