Where did the tabs on the browser start page go?

Question

Mozilla Firefox

Good afternoon. I recently encountered such a problem. On the start page, half of the tabs (bookmarks) disappeared somewhere. Chet couldn't find anything about this on google. Perhaps someone also encountered such a problem and knows how to solve it, or at least knows where they disappeared. There used to be 12 tabs, now there are 4. Where did they go - it's not clear. Thanks for any helpful information.
Screenshot:
https://yadi.sk/d/DeBjxpXk3G6jAB
UPD: I noticed in the css code of the main page that they added a property that closes the rest of the tabs:

#newtab-grid {
    max-height: calc(((100vh - 268.5px) / 15300) * 15300 + 7px) !important;
}