Firefox development lead, Mike Beltzner, has announced a slight change to the way Firefox opens new tabs, that will be featured in future releases.
Currently, when you open a link in a new tab it is added to the end of the tab bar, and the relationship with its parent tab exists only in the user’s head. I usually have to move it closer to the original tab to avoid tab scrolling.
With the new behavior, new tabs opened from a tab will be added to the right of the parent tab, unless there is already a child tab. In this case it is added to the right of the last child tab.
New tabs opened via the new tab button, File/New Tab… menu, Ctrl + T, etc. will still be opened to the end of the tab bar, as it is not possible to know if it’s contents will be related to the current tab or not.
Users of Internet Explorer 8 beta are already familiar with this behavior which also assigns a specific color to related tabs making it easier to identify them. The result, however, is a too colorful tab bar. Other approaches could be adding a small separator between tab groups, or a halo around or just below tab groups.
If you want to try this behavior, you can install Tabs Open Relative, a extension by John Mellor that does just this on Firefox 3. You will have to set extensions.tabsopenrelative.includenewtabs to false via about:config to have new tabs
I would also like to be able to press Shift while opening a new tab (via the main menu, a button, a keyboard shortcut or modifier), to force it open right to the current tab, so I can keep tabs together.
According to Mike, the new behavior will be added to trunk builds soon, but its inclusion in Firefox 3.1 is yet to be decided.