There is another manner of getting around this, I noted that FF started behaving erratically in the last week or two. There have been some updates in the background.

Top RHS of menu bar, there are 3 lines, click on it.
Then at the bottom of that menu, there is the "?", click on it
Look for "Troubleshooting Information", click on it
On the next screen there will be info, top RHS see the section that says :Give Firefox a tune up", below it press the "Refresh Fire Fox"

Fire Fox does some maintenance and clean up, and tends to work well again.
I have also found that googling with the problem you have with Fire Fox in the search line brings some excellent replies and solutions.