If you hate that clicking CLOSE TAB button on last tab in Firefox closes entire browser, do the following:
In URL bar, type about:config, in Search field, copy this string browser.tabs.closeWindowWithLastTab. Switch it to FALSE by double clicking the entry.
After you do this, clicking close button on last available tab will just close the last tab and leave browser available for further use with empty page.
Out of all browsers, only Opera insists on doing the old fashion way where closing last tab only closes that tab and nothing else. Respect to Scandinavians. Good choice. The rest is just copying from Chrome like they don’t have any own identity or design skills… Yeah Mozilla, I’m looking at you. You did it like Opera still until you decided to copy the feature from Chrome. Why, I don’t know… It was a stupid decision.