Firefox keeps changing open tabs to new windows - how do I stop this?

Do you have any tab related extensions installed that may be interfering with preference in Options > Tabs?

Start Firefox in Use Troubleshoot Mode in Firefox to check if one of the add-ons is causing the problem (switch to the DEFAULT theme: Tools > Add-ons > Themes).

• Don't make any changes on the Safe mode start window.

See:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems