I’m a reluctant and occassional user of Mozilla’s tabbed browsing feature. I agree with Matthew Thomas that tabbed browsing is cluttering the UI of Mozilla. It could have been easily predicted that Open in New Tab would start to appear everywhere that there was Open in New Window. This adds to the complexity of the UI for little gain: new windows and new tabs give almost identical results.
Tabs do have a killer feature that may explain why people enjoy using tabs: open links in background. The idea is simple–instead of having new tabs open and take focus immediately, you can click a few links and have the tabs load while you continue reading the current page. This more closely matches the behavior I want. When reading a page, I often open links in new windows so that I can look at them later and not be distracted from the current page. When doing this with new windows I have to explicitly return focus to my previous page.
Bug 56690 is working to allow background loading of new windows, much like the tabbed browsing feature. As with many UI bugs, there’s more discussion than coding going on. Yesterday, Jesse Ruderman posted a cool bookmarklet that converts all links on a page so that they open in new background windows. Unfortunately they would open in reverse order: the last one clicked would end up being topmost behind the current window. I tweaked his bookmarklet to create a new open behind bookmarklet. Mine places the windows in the background in the order they were clicked; the first one clicked will be the first one visible behind the current window.