You can use one close X at the far right end of the Tab bar and use that button if the tabs get small and you have difficulties to close a tab.

• http://kb.mozillazine.org/browser.tabs.closeButtons

Sorry, but I don't have difficulties to close a tab. I have difficulties to close the correct tab.

You can't disable the tab scrolling with the mouse wheel AFAIK, so you need to use other means to close the tab.
You can close the current tab with the close X on the tab or one close X at the end of the tab bar or use the keyboard with Ctrl+W.
Not selected tabs can only be closed via the right-click context menu as an alternative.

Otherwise you can try to set the minimum width of a tab to a larger value to have more room with the scrolling.

• Custom Tab Width: https://addons.mozilla.org/firefox/addon/custom-tab-width/

Thanks for reply. I tried this addon, but setting "minimum width" of tabs is useless. Wheel scrolling works by formula: TabWidth * 3 (multiplied by 3). So the larger the tab width, the more scrolling I get.

I solved my problem by setting "browser.tabs.closeButtons" option parameter to "2" in "about:config" page. Now all tab close buttons is turned off (do not appear).