Yeah, I saw that (the default for one of them changed to 5 for some reason). Searching around, I found this link:
https://wiki.mozilla.org/QA/Newtab_page_Tiles/Test_PlanIt looks like something about the tabs changed for Firefox 33, but I really can't tell what from that document. The two notable parts I saw were:
- If there is not enough space for the fixed size tile and it's gutters, rows and/or columns are removed from the grid.
- In the Tile Grid, there will be Top Sites tiles (based on user frequency), but also Sponsored or Partner tiles.
I don't know why the first one changed (as opposed to just scaling the tiles like they did before). The second one seems like a whole different scary thing.