Start Firefox in Abgesicherter Modus to check if one of the extensions is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

If it does work in Safe-mode then disable all extensions and then try to find which is causing it by enabling one at a time until the problem reappears.

• Use "Disable all add-ons" on the Safe mode start window to disable all extensions.
• Close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")

• https://support.mozilla.com/kb/Troubleshooting+extensions+and+themes

Hello

and thanks for your answer. I tested the following: 1. Start Firefox with deactivated add-ons, but not in safe mode

 => same faulty behaviour

2. Start Firefox with deactivated add-ons and in safe mode

 => Firefox works normal

3. I activated all add-ons step by step in safe mode

 => Firefox works normal again

Do you have another idea to solve this problem?

Thanks. Michael

If you are in Save mode mode then extensions are always disabled.

Are you in normal mode or in safe-mode in the topic marked as 3?

Hello,

1. I started in safe mode with deactivated add-ons (see picture 1) 2. View of the deactivated add-ons (see picture 2) 3. Then I try to activate the add-ons (see picture 3, with first activated add-on)

In Firefox 4 Safe mode disables extensions and disables hardware acceleration.

• Tools > Options > Advanced > General > Browsing: "Use hardware acceleration when available"

If disabling hardware acceleration works then check if there is an update available for your graphics display driver.

Hello,

that's the solution - thank you. I have the current driver for my Nvidia Quadro NVS450, so I deselect this option permanent. But Firefox works and that's all.

Regards Michael

You're welcome