I know I'm running Waterfox 18.0.1, but I wanted to report what I have seen in regards to this.
First, when I close Waterfox, the thumbnail directory, located here
When I re-open Waterfox, I have google as my homepage. The directory gets re-created, and in it I see two files showing the google homepage. As I continue to have Waterfox open, additional files (with a .PNG extension) will be added. But, once I close the browser, they are all removed, including the directory they are in.
Now, I know in my case, when I click on the New tab button (that little + sign next to my current tab), I get a blank screen. No thumbnails show up. But, I do see "spaces" so to speak where they could be.
I know the only modification I have made in "about:config" is this one
I change the value from the default "False" to be "True". This way, every time I exit Waterfox, an export file of my bookmarks (bookmark.html) is created in the root of my profile directory. If I ever need to re-install my OS, or more important, re-install Waterfox, that is the only file I need to save.
Outside of that, I have made a few changes to the actual Waterfox items (Tools then Options). However, I don't know specifically which one of them would cause it to work this way.
In any case, just wanted to point this out.
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