Same problem. Especially annoying when I have several tabs open but have minimized the icon to the taskbar. I can open it by left clicking on the small pop-up from the task bar and selecting maximize. It will then open to the full screen - but that's not how I want it. What's going on?

https://support.mozilla.org/en-US/kb/changes-toolbars-and-window-sizes-are-not-saved You may have corrupt xulstore.json or Localstore.rdf files.

Close Firefox. Open your file browser to this hidden location:

• Mac: *~/Library/Application Support/Firefox/Profiles
• Linux: *~/.mozilla/firefox/Profiles
• Windows: %AppData%\Mozilla\Firefox\Profiles
• *C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles
• Windows XP: C:\Documents and Settings\<user>\Application Data
  \Mozilla\Firefox\Profiles\

Search for the above files. Then rename or delete them. Restart Firefox.

Thanks for your reply. I was hopeful, but when I got to Profiles I did not find either of those files. What I found were files starting as folllows:

3arsfxjm.default

u7yaa9 06opmozs

Files, or folders? Use the search box to find those files.

Thanks., Found the xulstore file - it was in a folder called old Firefox data. I've deleted it. The localstore file was not found on my computer.

I hope this solves the problem. Many thanks.