Firefox Tips

Duplicate current tab

Ctrl + click Reload button

Configuration settings

about:config

JavaScript Errors

Tools/Error Console

Profiles Location

%appdata%\Mozilla\Firefox\Profiles

Change number of results in URL bar

Change browser.urlbar.maxRichResults value in about:config.

See "Browser.urlbar.maxRichResults - MozillaZine Knowledge Base." Knowledge Base - MozillaZine Knowledge Base. Web. 16 Sept. 2011. <http://kb.mozillazine.org/Browser.urlbar.maxRichResults>.

Set Ctrl + Tab to go to most recently used (MRU) tab

Note: This is similar to the IE9 setting "Use most recent order when switching tabs with Ctrl+Tab".

Firefox 5
1) Change browser.ctrlTab.previews to true in about:config.

See "Making CTRL+TAB to go to Most Recently Used Tab • mozillaZine Forums." Web. 2 Aug. 2011.
<http://forums.mozillazine.org/viewtopic.php?f=23&t=2136713>.

Close Button on Last Tab Missing in Firefox

Firefox 5
1) Change browser.tabs.closeWindowWithLastTab to false in about:config.
Firefox 3.5
1) Change browser.tabs.closeWindowWithLastTab to false in about:config.
2) Add the following to userChrome.css:

.tabbrowser-tabs[closebuttons="alltabs"] > .tabbrowser-tab > .tab-close-button
{
display: -moz-box !important;
}
.tabbrowser-tabs:not([closebuttons="noclose"]):not([closebuttons="closeatend"]) > .tabbrowser-tab[selected="true"] > .tab-close-button
{
display: -moz-box !important;
}
See: Show Close Button In Last Tab with Firefox 3.5 | Joe Riggs Bloggs
http://joe-riggs.com/blog/2009/07/show-close-button-in-last-tab-with-firefox-3-5/

Updates

2014-04-01 Added "Duplicate current tab"

2011-09-16 Added "Change number of results in URL bar"

2011-08-02 Added "Ctrl + Tab" section.

2011-07-19 Added Firefox 5 "Last Tab Missing" step.