Do you recall what version you were running before? '''''Links and Tabs''''' By default, Firefox intercepts links that sites send to a new window and opens them in a new tab instead. Sites do that in two ways: * Setting a target attribute on the link, such as target="_blank" * Using the script method window.open(), which creates a popup window But when a site has not specially coded the link, you would normally have to divert it to a new tab yourself by holding down the Ctrl key when clicking, or middle-clicking with the mouse scroll wheel. There is an add-on to take care of that automatically ("Open Link with New Tab"): https://addons.mozilla.org/firefox/addon/open-link-with-new-tab/ After installing, you need to use the Add-ons page to set your preferred behavior. Either: * Ctrl+Shift+a (Mac: Command+Shift+a) * "3-bar" menu button (or Tools menu) > Add-ons * type or paste '''about:addons''' in the address bar and press Enter/Return In the left column of the Add-ons page, click Extensions. Then find the extension on the right side and click its Options button or More link. That should take you to the panel where you can adjust its settings. ''Scripted Popups'' If scripted popups launch in a new window instead of a tab, see: https://support.mozilla.org/questions/1109391#answer-842979 '''''Bookmarks and Tabs''''' Left-clicking a bookmark normally open it in the same tab; you can hold down the Ctrl key to direct it to a new tab, or middle-click it with the mouse scroll wheel. There is a setting to change that so you get a new tab for a regular left-click: (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk. (2) In the search box above the list, type or paste '''tabs''' and pause while the list is filtered (3) Double-click the '''browser.tabs.loadBookmarksInTabs''' preference to switch its from false to true