The implementing of my regular extensions into Firefox 2.0 seems to have gone beyond just TabX: there’s no more need for Session Manager or undoclosetab either.
Looks like SwitchProxy no longer works, but FoxyProxy promises to do so, and also offer more features than SwitchProxy or in fact any other such extensions. Paste And Go has been superseded by Paste And Go 2. Greasemonkey‘s said to be compatible with only up to 2.0b1 for now.
For a while, I thought the tab closing ‘x’ button was only available on the active tab, but then I discovered browser.tabs.closeButtons, and was confused, as it was set to ‘1’ as it should be in order to Display close buttons on all tabs
and not just the active one. I then discovered browser.tabs.disableBackgroundClose, which my about:config didn’t have, and set it to false, just to be sure. No effect.
The reason behind the vanished closer buttons turned out to be browser.tabs.tabClipWidth. TabX had no such value, so that the closers were always visible. I decreased the default value of 140 down to 70 for starters, but I might have to set it down all the way to zero to retain the feel of TabX.