I can't be specific but it could be due to malware. Although the following is about crashing rather than freezing, it would be worth a look: https://support.mozilla.org/en-US/kb/firefox-18-crashes-startup-due-malware-how-fix

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode

Try to disable hardware acceleration in Firefox.

• Tools > Options > Advanced > General > Browsing: "Use hardware acceleration when available"
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

• https://hacks.mozilla.org/2010/09/hardware-acceleration/

Thanks, when i disabled the hardware acceleration it works again.

You're welcome

The context in which the problem occurs is necessary for me to know whether it has been fixed. Safe mode or reset is not a solution. Ever.

All these solutions do is allow Mozilla to wash its hands. If Mozilla has changed something that suddenly makes addons fail it is a FF bug and it is on Mozilla to find and fix the problem.