Always check if Firefox is your default browser: Select this setting if you want Firefox to check whether it is the default browser at startup. Making Firefox your default browser will ensure Firefox is used, whenever an application tries to display a web page.
Save files to: If selected, Firefox will automatically save all downloads to the specified folder (such as the desktop or your downloads folder). To change which folder is used, click Browse…Choose….
Always ask me where to save files: If selected, Firefox will ask you to select a folder for every download you wish to save.
Ctrl+Tab cycles through tabs in recently used order: Select this optionpreference if you want to use the Ctrl + Tab keyboard shortcut to switch through your open tabs in the order you viewed them rather than in the order your tabs appear in the Firefox window.
Open new windows in a new tab instead: This optionpreference controls whether links from other applications or from web pages which request to open them in new windows are opened in a new window or a new tab in the most recent window.
Note: If you have chosen to open pages in new tabs, Firefox will ignore this optionpreference and will open a new window from a link if the page author specified that the new window should have a specific size, because some pages can only be displayed correctly at a specific size.
(If applicable)Warn me when closing multiple tabs: This optionpreference is only shown if you disabled the warning dialog Firefox displays to confirm your choice to close a window with multiple tabs (shown below). Check this optionpreference to re-enable the warning, to prevent accidentally closing the entire window when you only intend to close the current tab.
Note: This setting has no effect on the warning when closing other tabs in a window.
(If applicable)Warn me when opening multiple tabs might slow down Firefox: This optionpreference is only shown if you disabled the warning dialog Firefox displays to confirm your choice to open multiple tabs at once. Check this optionpreference to re-enable the warning, to prevent accidentally slowing down Firefox while loading a large number of tabs.
Don't load tabs until selected: Firefox will only load the active tab when it starts or restores your previous session. This can make startup much faster if you are restoring many tabs. The other open tabs will be loaded as you click on them.
When I open a link in a new tab, switch to it immediately: When you middle-click on a Web link (or hold down Ctrlcommand while clicking with the left mouse button), the page will be opened in a new tab. That page will not be displayed and will load in a background tab. Check this optionpreference to load and display the page in a new foreground tab instead.
Show tab previews in the Windows taskbar: When you move your pointer over the Firefox icon in the Windows taskbar, Windows will show you a preview of the Firefox window. With this option check marked, Windows will show you a separate preview for each tab.