https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode

Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes). If the problem goes away, that tells us one thing. If it does not, that tells us something else.

It could be Hardware Acceleration. How to disable Hardware Acceleration {web link}

I had tried disabling hardware acceleration and it didn't fix it.

Keep in mind that the problem does not occur when I use a different profile which has the same add-ons and plug-ins, and uses hardware acceleration.

If I enable the add-ons and plug-ins while in safe mode, the problem does not occur. Safe mode is changing something else in the profile that is eliminating the problem.

Try to uninstall Adblock Plus and possibly try uBlock Origin instead. https://addons.mozilla.org/firefox/addon/ublock-origin/

If you use a userChrome.css file in the chrome folder in the profile folder then try to rename/remove this fill (userChromeSAV.css).

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Gave that a try. No joy. Thanks for the suggestion.

I have already uninstalled Adblock. No help. I really don't think it has anything to do with add-ons.

I would suggest creating a new profile. Copy the bookmarks and password files to the new profile but nothing else.

Add-ons should be downloaded fresh.

You did close and restart Firefox after disabling hardware acceleration in Firefox?

Yes, I restarted Firefox after disabling hardware acceleration.

I can download files from some sites (NZBIndex.com), but cannot download from others (CNet.com). It seems to be whether the file is simply downloaded to my download directory as soon as I click on "download", or whether a pop-up window asks me whether I want to save or run the file (this is when it fails).

If I use a different profile, it all works fine, so the problem is obviously in the Root Directory profile (I have one profile which does not have a Local Directory, and it works).

I appreciate all you assistance. I really hate to go through all the hassle of reinstalling the program and trying to salvage the data files.

Could it be possible that the window is too large and that these buttons fall off at the bottom? Can you zoom out this window or possibly open its system menu via "Alt+Space" and resize?

"The buttons fall off"? I can't figure out if this is supposed to be a joke.

https://support.mozilla.org/en-US/kb/changes-toolbars-and-window-sizes-are-not-saved You may have corrupt xulstore.json 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 it. Restart Firefox.

FredMcD has got it - mostly.

When I renamed the xulstore.json file, it resolved the issue I presented. Congratulations and thank you very much. Unfortunately, all of my formatting has gone away, but that can be resolved easily (I hope).

Thank you again.

I mean that these buttons are not visible because they do not fit in the file picker pop-up window. Did you try whether it is possible to open a system menu via "Alt+Space"?

Can you attach a screenshot?

• https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem
• use a compressed image type like PNG or JPG to save the screenshot

Try to rename/remove xulstore.json and when present delete localstore.rdf in the Firefox profile folder with Firefox closed.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

_Howard said

Unfortunately, all of my formatting has gone away

Sorry, but you will have to restore them manually.

Back up and restore information in Firefox profiles.{web link} I use an add-on that makes backups of my user profile, Just In Case. Unfortunately, it is not compatible with the current Firefox.

Every now and then, open the profile folder and create a copy of the current profile as is to another location on your hard drive. This way you will have a backup.

If you do this each day, you will not lose much data. This should be done with Firefox Closed.

Note: In case you need to restore from these backups, you may need to overwrite old or corrupted files.

Five minutes and I had the formatting restored.

I do make backups of everything in AppData once a week.

The last update of Firefox is where I ran into this problem.

But all is fine now, and I want to express my appreciation for all your assistance.

Glad to help. Safe Surfing.