Try one of these articles:
- Refresh Firefox - reset add-ons and settings Restore Firefox to its default settings while saving essential data. This can fix slowness, crashing, search hijacking and other problems.
- What do the SSLv3 error messages mean on Firefox? When accessing a site with SSLv3, Firefox will block it and display an "Unable to connect securely" message.
- Firefox Health Report - understand your browser performance Firefox Health Report lets you know how well your browser is performing and what steps you can take to improve it.
- Firefox is slow after updating to Firefox 38 If Firefox 38 is slow to respond after the recent update, disabling hardware acceleration or updating your graphics driver should help. Here's how to do that.