Hi chaac, there are a variety of scenarios that Firefox treats differently: (1) Links in pages in Firefox that target a new window, but don't restrict window features The box you checked should work to divert those pages from a new window to a new tab instead. You can uncheck and check it again to make sure it is set. (2) Links in pages in Firefox that target a new window and set restrictions like window size Firefox shows a popup without the regular toolbars. Are these the problem? (3) Links or shortcuts opened outside Firefox Normally Firefox will follow your setting for #1, but there is a separate option for these. Also, there can be an issue with your Firefox configuration that causes external links to open in a different profile (i.e., different settings, toolbar layout, history, add-ons). Are you having a problem with external links?