You may have several issues. Let's start with;

https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

Note: Some software, like Advanced SystemCare with Surfing Protection, can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

Hi Fred,

Thanks for your advice.

I do indeed have Advanced System Care with Surfing Protection, but I tried turning it off and then reinstalling Firefox, but no change—same problem.

Again and again I see the advice to go to Troubleshooting Information and click on the Refresh Firefox button. I have NO Refresh Firefox button in Troubleshooting Information. All I see in the upper right corner is “Try Safe Mode” with a button that says “Restart with Add-ons Disabled”. What happened to Refresh Firefox?

Here’s a possible clue. I next was going to try the advice of editing the user.js file. When I tried to open it, I got the attached error message. I have no idea what it means.

Another possible clue is that just when this problem started yesterday, I started getting the attached error message every time I restarted my computer. I have no idea what this means either. Maybe it’s related. Maybe not. I have never used anything called Qt platform and have no idea what it is.

Apart from these two things, my computer seems very healthy and everything is working normally. I really am desperate to get Firefox working again because right now I have no bookmarks. I hope if I can ever get Firefox to work again, that I’ll be able to restore the bookmarks. I appreciate your help.

Carl

I called for more help.

The 'user.js' error I think means the file was corrupt. I don't know about OneDrive.

Use these links to create a new profile. Use this new profile as is. Is the problem still there?

http://kb.mozillazine.org/Profile_folder_-_Firefox#Navigating_to_the_profile_folder

https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

Type about:profiles<enter> in the address bar.

Hi Fred,

Thanks, but I have created at least a dozen new profiles in my attempts to solve this problem over the last two days, and nothing changes. If I create a new profile and try to open Firefox, it won't open. If I reinstall Firefox and presumably have a new profile, it won't open. The only way I can open Firefox is to create a new profile and rather than open Firefox the usual way, click on the Open Firefox button in the Profile Manager.

First of all, I don't know what a .js file is (Java Script?), but wouldn't a new installation have a new and not corrupt .js file? Is Java Script something that can be reinstalled? I've heard of it, but I don't know what it is.

And second, it seems like the profile folders that cannot be made so they are not read only must have something to do with this? I gather from my research that this has been an issue for many people for many years. How it cannot have been fixed by Mozilla or Microsoft by now puzzles me. It also puzzles me how Firefox could have worked perfectly and then in an instant malfunctioned so badly that even reinstalling it doesn't fix the problem. Other programs create logs and error reports of various sorts. Is there something like that that I could find and send you.

I appreciate your help, but I'm worried that I'm going to end up wiping out my entire computer and having to reinstall everything.

I followed the advice in number 4 of this page:

http://answers.microsoft.com/en-us/ie/forum/ie8-windows_xp/how-do-i-reinstallrepair-a-corrupt-javascript/dc0ad96d-eb6c-44b7-9dc2-2c3d59fabb2c

and when I ran the second one, I got the attached error message. I haven't got a clue what it means, but I'm going to Google the error code and see what I get. Does it mean anything to you?

Delete a possible user.js file and numbered prefs-##.js files and rename (or delete) the prefs.js file to reset all prefs to the default http://kb.mozillazine.org/Preferences_not_saved

Sorry, but that didn't work. I deleted the user.js and the prefs.js and the several numbered prefs-##.js files and here's what I get:

Your Firefox profile cannot be loaded. It may be missing or inaccessible.

I noticed there was no new numbered prefs file created, so I created one using the Profile Manager. As always, I could then open Firefox using the button in the Profile Manager, but after closing and attempting to open, it was the same problem--probably because the pref file became read only after closing Firefox. I'm going to try to fix the JavaScript error message. That must be related somehow.

carlwhart said

the pref file became read only after closing Firefox.

No Firefox file or folder should be Read Only. This is not Firefox doing that.

Check your protection programs. Some are known to 'protect' Firefox files. Tell those programs to leave Firefox alone.

Hi Fred,

For reasons that are a complete mystery to me, Firefox, after yet another reinstall, seems to be working. At least I can open it successfully without getting a message about not being able to open because the profile folder can't be found.

I already tried turning off surfing protection in Advanced System Care, and that made no different. I don't have Norton 360, but I do have Norton Security which has a section called Firewall Program Control. Firefox was set to "Allow". I turned it off and on again, and maybe that reset something. Who knows? It's as good a guess as any. I still suspect the error message I get at start up about OneDrive not finding the Qt platform plugin "windows" must be related somehow. When I ran the javascript diagnostic I discussed above, I got an error message which led me to discussions of "stack overflow", and every discussion I see of how to fix this Qt platform problem also mentions "stack overflow" and javascript. It's all incomprehensible to me, so it doesn't really help. But someone else might benefit from this bit of info.

Now my question is how do I restore all my bookmarks, add ons, etc. I made a backup of my original profile folder. I could flounder around and experiment, but I really rather have someone who knows what he's doing tell me. I appreciate the time you've taken to try to fix this. I hope it continues to work. I won't be surprised if this happens again.

That was very good work. Well done. Please flag your last post as Solved Problem so others will know.

When you are ready, we can start moving parts of your old data and Copy it to the new profile.

First; open your file browser to the New profile;

Type about:support in the address bar and press enter.

Under the page logo on the left side, you will see Application Basics. Under this find Profile Folder. To its right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.

Second, open another file browser to the Old profile.

Warning ! ! Only Copy the files you are told. We will avoid anything that might be the cause of your problems. Here is the list of files;

cookies: cookies.sqlite Do not bother. Cookies will be created when you return to the website. However, you will have to log in everywhere. And you may lose any settings that websites store on your computer.

extensions(add-ons, themes): it would be better to download them fresh. +++++++++++++++++++++++++++++++++++++++++++++++++ key3.db and logins.json : These are the Password files. Copy Both !

persdict.dat : custom dictionary – words you added to the dictionary

mimeTypes.rdf : What to do with what type of file.

places.sqlite : History and Bookmarks.

prefs.js : Your settings. Note, If you were having problems, this could be contaminated.

cert8.db and possibly cert_override.txt : Stores all your security certificate settings and any SSL certificates you have imported into Firefox. If removed, the file will be replaced.

search.json.mozlz4 file stores the user-installed search engines that are available in the Firefox v47+

search.sqlite file and searchplugins folder store the search engines that are available in the Firefox Search bar before Firefox v47 +++++++++++++++++++++++++++++++++++++++++++++++++ Copy these files from the old to the new. You will get a message that the files already exist. Choose to over-write for each file.