From MozillaZine Knowledge Base

Possible values and their effects

Description Problem - Although written here exactly as Mozilla describes, the description -

1 Display close buttons on all tabs (Default) is not accurate. In Firefox, depending on tabbar length, only a total of around 8 tabs have close buttons if this entry is used, add one or two more tabs and none do and after that, the tabbar goes into 'tab overflow' mode with tab arrows, where again no tabs have close buttons.

As this article is directly concerning about:config entries only, then I think that pointing out this mis-description directly in the article is outside the remit of it. However, the solution (which could be pasted elsewhere?) is to add - .tab-close-button { display: -moz-box !important;} to userChrome.css, which does then give a true 'close tabs shown on all tabs' type situation. :) --Frank Lion 00:25, 23 July 2009 (UTC)

I did a search on this preference and says:
 347 // Where to show tab close buttons:
 348 // 0  on active tab only
 349 // 1  on all tabs until tabClipWidth is reached, then active tab only
 350 // 2  no close buttons at all
 351 // 3  at the end of the tabstrip
 352 pref("browser.tabs.closeButtons", 1);
Go ahead and change the description to agree with the above if it's more accurate. I don't know about adding a userChrome.css solution to the article, though, since adding such things is probably outside its scope (see Category talk:Preferences for an outline of what goes into these articles) but see if anyone else thinks you should go ahead. If you want to add something to the KB on UserChrome additions, you could also do what dickvl does, add such things to your user page, which is now blank, then you could link to it, or even create some KB articles under Category:Configuration. Alice 01:16, 23 July 2009 (UTC)