I've got some add-ons. GisMeteo Toolbar is among them. I'm not use it, but it allows to use a button in the top-right corner of Firefox. So, I'm try to switch off the toolbar. Some time ago this works, but now the toolbar appears again after restart firefox. What's wrong? Is it toolbar problem or firefox problem?
If an extension places content (info) on the Add-ons bar then it is possible that the Add-ons bar will be displayed to make you aware of this. You will either have to move this data to another toolbar if possible or disable the extension(s) that cause this.
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.