Try one of these articles:
- Refresh Firefox - reset add-ons and settings Repair or tune up Firefox by restoring it to 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.
- How to reset the default user agent on Firefox How to set your user agent back to default