Your browser reported your OS as Windows XP. Is that correct? And you currently have Firefox 52 ESR, the latest Firefox that runs on XP?

Before proceeding, please make sure you can view hidden files and folders:

• XP: https://kb.wisc.edu/helpdesk/page.php?id=8036
• 7-10: https://support.microsoft.com/en-us/help/14201/windows-show-hidden-files

Next, if you haven't already, please check the following article (probably the section on restoring a backup won't help:

"Firefox is already running but is not responding" error - How to fix

The following section may also be relevant (parent.lock file):

http://kb.mozillazine.org/Profile_in_use#Remove_the_profile_lock_file

Any luck?

I still cannot access firefox. keeps telling me to close my browser.. but I can't find where it is. I think I accidentally downloaded the new firefox and it is not compatible with my XP. can anyone help?

So there is no firefox.exe in the Windows XP Task Manager that you can select and kill using "End Process"?

And there is no file named parent.lock in your current Firefox profile folder?

If that's true, hmm, does shutting down and restarting Windows help?

If all else fails, you could temporarily hide all your Firefox data from Firefox, and it should start up looking like a new install.

However, I think it's a good idea to double-check your current version. If you go to the Firefox program folder, right-click firefox.exe, click Properties, then click the Details tab, the version should be indicated there. The Firefox program folder on XP is here:

C:\Program Files\Mozilla Firefox\

Then if you need to hide your Firefox data, load this "shortcut" path:

%APPDATA%\Mozilla

That should expand to this hidden folder path

C:\Documents and Settings\username\Application Data\Mozilla\

In that folder, right-click Firefox and choose Rename. Then change the name to FirefoxOLD.

The next time you start Firefox, it should generate a fresh profile so you're up-and-running. Migrating over your data will take some time, but here are some articles to get you started:

• If you just want bookmarks: Restore bookmarks from backup or move them to another computer -- use the "Choose File" option to point Firefox to the bookmarkbackups folder in the old profile (under FirefoxOLD if you drill down a few levels)

• If you want most of your data: Recovering important data from an old profile