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

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,

Deleting the xulstore.json, will set ff to maximized when you start it again, then when you resize it, it can remember its last window size, but setting it again to maximize then close it again, it will just open again but not maximized.

How to reproduce: 1. delete the xulstore.json 2. open ff, it will now open maximized 3. resize it, and close 4. open it again, it will now open with the last window size 5. now maximize it and close. 6. It will now open but not maximized.

I called for more help. When Firefox is closed, it records the window position and size. But something is interfering with this.

zer09 said

5. now maximize it and close.
6. It will now open but not maximized.

Open Firefox. Set the window to max. Then Close Firefox.

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?