OK, I found extension's name: Fast Dial, and mozilla displays that it's old. How can I get access to my bookmarks stored in it? And next time, when you release an update, please make it backwards compatible, or at least notify users that their extensions won't work and ask if they really wish to update.

No one responded? I've already got an answer from FastDial's author: there is "FastDial" folder in normal bookmarks.

Sorry we are under a back log of questions. So then you have found what you needed from the Developer that's great. As that is what would have happened here , would have sent you to the Developer to find out. Mozilla only ok's addons/Extensions for use then provides them with a Web Page to Distribute from.

So you have solved this then. If so Mark this as solved with you as the solution.

If not please let us know.

No, I haven't solved it. I haven't installed FastDial to open these sites from bookmarks, but to have quick access to them when opening a new tab, and you made Mozilla incompatible with it. I don't want Mozilla to control shortcuts to which sites I have on my new tab, I want to control it myself again. Imagine you can't choose shortcuts you have on your PC's desktop or Android homescreen, but your OS decides about it for you, generally suboptimally.