Firefox: You can only fit so many tabs in Firefox's tab bar until it makes you scroll through them. With Custom Tab Width, you can change the maximum and minimum tab width and fit more tabs in the tab bar at once.
When you open a lot of tabs in Firefox, you have to start scrolling through them with a button on the right side of the tab bar. If you prefer the way Chrome handles tabs — that is, it just makes them smaller and smaller and smaller so they all fit in the title bar — Firefox extension Custom Tab Width will let you do so. Just install it and set the maximum and minimum tab width in its preferences. I found 40 was a pretty good minimum width (you can set it to 1, but then the graphics get pretty messed up).
Custom Tab Width is a free download for Firefox 4. If you want the same functionality in Firefox 3, you can do it by setting browser.tabs.tabMinWidth and browser.tabs.tabMaxWidth in about:config.