hello, this sounds like an issue with adware on your system, so please perform all these steps:

1. refresh firefox (this will keep your bookmarks and passwords)
2. afterwards go to the firefox menu ≡ > addons > extensions and in case there are still extensions listed there, disable them.
3. finally run a full scan of your system with different security tools like the free version of malwarebytes and adwcleaner to make sure that adware isn't present in other places of your system as well.

Troubleshoot Firefox issues caused by malware

That was the first i tried :( But yes ist an adware Problem, i will try to find a way then

After a Refresh, Firefox will rediscover some add-ons that were installed in shared folders (outside of your personal Firefox settings). While you're reviewing, check for a possible bad extension.

You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Extensions. Then cast a critical eye over the list on the right side. All extensions are optional. If in doubt, disable.

Often a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step.

Any improvement?

If the unwanted page appears only when you use your desktop shortcut or pinned Taskbar icon, and not when you launch a new window from within Firefox (Ctrl+n) or use the Home button, check for a hijacked icon:

The Firefox icon (like other browser shortcuts) can be set up to launch specific pages at startup (or more specifically, when you use the icon). To check whether that is set:

First, open the shortcut as follows:

• Desktop shortcut: right-click the icon, choose Properties
• Pinned taskbar icon: right-click the icon, right-click Mozilla Firefox, choose Properties

Windows normally will select the Shortcut tab. If not, go ahead and click the Shortcut tab.

You'll see the Target highlighted. On 64-bit Windows, that usually is no more and no less than the following:

"C:\Program Files (x86)\Mozilla Firefox\firefox.exe"

If anything follows after that, try clearing it out.

After OK'ing the Properties dialog, you can test right away to confirm that Firefox now launches only your home page. Either:

• double-click desktop shortcut
• right-click pinned taskbar icon, click Mozilla Firefox

Success?

I found reason for the issue it wasnt an issue with Firefox it was a Virus in Internet Explorer that has rewrittwen the download from Mozilla that is why i wasnt able to fnd a solution for Firefox itself.

oh i meant nice search not quick search my misstake