This is not unusual behaviour. Firefox is always adding, changing and deleting files within your profile folder. My assumption is that the read-only box is not actually checked, but rather it contains a black square or dot. That doesn't mean that everything in the folder is read-only, just that at least 1 thing is.

A good example would be this. If you mark the folder as read-only and then Firefox adds a new file into the profile (a temporary file, a backup, etc), then the read-only will get the black mark.

In addition, I believe there are also files that Firefox will constantly monitor and change back to read-only. This is because not every file can or should be modified. You can actually damage your profile by doing that.

Now, to address what I believe is the main purpose of your question: solving the "Firefox is already running" error. This is a common message to see when you close Firefox and start it up again. This is because there are certain tasks that Firefox needs to complete in the background even after you have closed it.

For example, it may need to save your session so it can restore it when you open Firefox again. This takes time, so opening too quickly can cause this issue.

That said, it's not normal to see this message if you closed Firefox a long time ago or if you are opening Firefox for the first time since your computer was turned on.

Common quick fixes could include rebooting your computer or trying to disable add-ons that may be slowing down Firefox and trying to run in the background. I don't believe that the read-only status of your profile folder has anything to do with the issue you are having.

Hope this helps.

You can ignore a green block for the read-only attribute. Only a real checkmark (√) means that the folder and all its content is read-only. Windows doesn't check this and simply shows a green block by default. You need to check each file to be sure (i.e. use List view and make the attribute column visible).

Original problem: "Close Firefox. Firefox is running but does not respond. Old Firefox must be closed to open new window".

The unchecked box problem resulted in trying to fix the problem from a Firefox solution that said to uncheck the box (see attachment). That fixed the problem but the box will not stay unchecked. If the box stayed unchecked, my problem would be solved.