It might be happened because of corrupted files

• xulstore.json or Localstore.rdf

Quit your Firefox and open the profile folder using the below command.

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

Find the below file name in the profile folder and Delete those files, before deleting Quit your Firefox.

• xulstore.json
• Localstore.rdf

For more info: https://support.mozilla.org/en-US/kb/changes-toolbars-and-window-sizes-are-not-saved

Thanks. I did see some odd profile and file info. I think it was the Localstore file that may have been it. I already see a difference. Addition: But the difference didn't stay sticky. See new note below.

There were two xulstore files, one from today and one from 2015. Also, no Localstore.rdf, but:

localstore-safe.rdf from 2014 localstore-safe.rdf from 2010 localstore-1.rdf from 2012.

Deleting all three of these seems to have made a difference.

The changes didn't stick. Browser launch is back to full height with the top toolbar and half the tabs going off the top of the screen.

I guess the next step is to start looking at plugins: Adobe Acrobat Pro Flash and Video Download Mute Tab NoScript Page Screenshot uBlock Origin User-Agent Switcher

This only started happend with the last version or two of Firefox, so I am curious what else changed.

Your settings are not saved. try with new profile.

Create a new profile as a test to check if your current profile is causing the problems.

See Creating a profile:

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over the problem

Profile Backup and Restore

• http://kb.mozillazine.org/Profile_backup
• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Will try with a clean profile. Just to be clear, the settings do get saved, but then revert back. I can resize the window and either file->exit or click the X window exit and the settings do get saved. It's only after some period of time that it gets reverted.

There is a copy of Norton Antivirus and Tasks set to Automatically cleanup:

Chrome temporary files Interenet explorer temporary files Windows temporary files Internet Explorer history Disk Optimization

There wouldn't be any dependency on those things for Firefox, correct?

Posted yesterday but it seems to have gone into the bit bucket. Apologies if this appears twice.

Similar behavior seen here on 2560x1440 ThinkPad display @ 175% scaling. Same thing with 63.0 and 62.03. Maximizing vertically by dragging bottom of browser to top of taskbar works, but subsequently browser window becomes oversize - often obscuring the browser's tab bar.

60.3esr does not do this. It does revert to earlier versions' behavior: bottom of browser doesn't quite reach the top of the taskbar - the same behavior as the current Thunderbird. Not ideal, but much better that going oversize.

It's almost as if every launch it increases the size like it's miscalculating or mis-storing the settings based on either the scaling or the Menu and Bookmark bar.

That's good info about the version numbers. So much has changed since that version, but hopefully it can be isolated. I guess we both should try to figure out a series of steps to reliably replicate it. I've been able to rule out Norton system maintenance and the Add-ons.

I think I've been able to isolate it.

enable both Toolbars bookmarks and menu Launch firefox. Quit by close window top right X Launch firefox. repeat until window goes off top of screen.