Firefox won't open but it thinks it's open then it won't open because it says it's already open

After the latest update I gave up on Firefox and switched to Chrome which was already installed on my iMac. I didn't like Chrome and wanted to go back for firefox however it won't open but it thinks it's open somewhere. I also tried putting it in the trash and download a fresh install but the result was saying it won't open now because it's already running. How is that possible? Firefox always has to be forced quit which I did but now I'm more frustrated and confused than before.