hello, where does the home button take you to? please try entering about:config into the location bar of the browser and put the name of your former homepage (like oldhomepage.com) into the search field. do any preferences show up after that, that have your old home page as part of their value - if so, right click the entry & reset it to the default.

in case this does not bring a solution please also Diagnose Firefox issues using Troubleshoot Mode launch firefox in safemode once and see if the problem is occuring there too & report back with your findings. thank you.

Turns out that the problem was the identification of "Home" within the name "Home" on my bookmarks toolbar. When I clicked on the icon home to the right of the location bar, it always took me to the correct newly identified home page. But if I clicked on the name "home" on the bookmarks toolbar, it went to the old location.

So, voila, I changed the identification of that bookmark and the problem was solved.