Your comments

Thanks for the information, but I'm a bit confused about something you said.

"Once we finish fixing major problems, we will launch a new update. Most likely you will have the same problem again."

Does this mean that you expect that after you release a new update you still expect the problem with the background resetting to default, to not be fixed?

Unfortunately this fix fails. After I rename the profile folder, Firefox does not start and has the following error.

"Your Firefox profile cannot be loaded, It may be missing or inaccessible."

I've now changed the folder back to its original name.

I had the same issue yesterday evening, so within about 24 hours of installing the latest version. The dials were fine, but both the background image and the parallax settings were set to default on one of the restarts of Firefox.

It's only occurred once in the last few hours that I've been using it, so it would be difficult to catch it.