Firefox tab close button on all tabs

Visibility of tab's close button can be set by modifying browser.tabs.closeButtons through about:config. The values are:

// Where to show tab close buttons:
// 0  on active tab only
// 1  on all tabs until tabClipWidth is reached, then active tab only
// 2  no close buttons at all
// 3  at the end of the tabstrip

The problem is, that when browser.tabs.closeButtons is set to 1 the close button visibility depends on the opened tab number. If there are more tabs than the tabbar can show it goes into overflow mode and thus the tab close buttons are gone. This can be fixed by adding a few lines to your userChrome.css:

.tab-close-button { display: -moz-box !important; }
.tabbrowser-tab[pinned] .tab-close-button { display: none !important; } /* hide close buttons on app (pinned) tabs */

Remove custom items from Firefox bookmark menu

If you want your Firefox bookmark menu to display only your own bookmarks without all those "Bookmark This Page" items, go to %AppData%/Mozilla/Firefox/Profiles/profilename/chrome and edit userChrome.css. If it's not there, just create it. Now paste this:

#menu_bookmarkThisPage,
#subscribeToPageMenuitem,
#subscribeToPageMenupopup,
#menu_bookmarkAllTabs,
#bookmarksShowAll, #organizeBookmarksSeparator,
#bookmarksToolbarFolderMenu,
#bookmarksToolbarFolderMenu+menuseparator,
#bookmarksMenuPopup menuseparator[builder="end"],
#menu_unsortedBookmarks { display: none !important; }

#BMB_viewBookmarksToolbar, #BMB_viewBookmarksToolbar+menuseparator,
#BMB_bookmarksShowAll, #BMB_bookmarksShowAll+menuseparator,
#BMB_bookmarkThisPage,
#BMB_subscribeToPageMenuitem,
#BMB_subscribeToPageMenupopup, #BMB_subscribeToPageMenupopup+menuseparator,
#BMB_bookmarksToolbar, #BMB_bookmarksToolbar+menuseparator,
#BMB_bookmarksPopup menuseparator[builder="end"],
#BMB_unsortedBookmarks { display: none !important; }

#appmenu_showAllBookmarks, #appmenu_showAllBookmarks+menuseparator,
#appmenu_bookmarkThisPage,
#appmenu_subscribeToPage,
#appmenu_subscribeToPageMenu,
#appmenu_subscribeToPageMenupopup, #appmenu_subscribeToPageMenupopup+menuseparator,
#appmenu_bookmarksPopup menuseparator[builder="end"],
#appmenu_unsortedBookmarks { display: none !important; }

The last part (in orange) will hide default items in Firefox appmenu bookmarks as well, so leave it out if you want to customize bookmark menu in  a toolbar only.

Hide native element inspector in Firefox 13+

I don't know why but Mozilla decided to not allow Firefox users to disable their native element inspector. It really gets in the way if you are using Firebug. Fortunately, Firebug allows us to hide it in the about:config page. Just change this value to false:

extensions.firebug.hideDefaultInspector