you mean home page?

I'm not sure, but perhaps it is this problem that occurs with Flash in Windows 7: when you open a new Window that uses Flash, if no other tabs have used Flash in the past 3 minutes, Firefox will switch to showing the last active Window. More info and workarounds: Opening New Windows and Shockwave Flash.

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