From MozillaZine Knowledge Base
Many of these tips come from Firefox support.
A Mouse Wheel Click can be used wherever a Middle Click is required in the tips below. For those without middle mouse buttons or mouse wheel, clicking both mouse buttons at the same time also mimics the Middle Click function. Many Laptops mimic the Middle Click function if you click the right and left pads at the same time.
Logitech Wheel button and SetPoint software
By default, when SetPoint is installed, the wheel button doesn't seem to work at all. The following settings seem to allow for the Wheel button to work as intended in Firefox:
The wheel button should now work as expected. If not, try restarting Firefox.
Middle Click on a link will open that link in a new tab. This principle will work in many other situations, such as on bookmarks, bookmark folders, history items, page images, and also on toolbar buttons such as Home, the Back and Forward buttons, Personal Toolbar items, and the Throbber [the 'busy' icon at the top-right]. Moreover, you can even Middle Click on menu items which represent web page (such as items from the Back, Forward, Bookmarks, Go, and View Image menus) to open them in a new tab.
Middle Click on a tab marker will close that tab.
Note that user preference "middlemouse.contentLoadURL" must be set to false (default for Windows version) for this to work. To verify that the preference is set to false, enter "about:config" in the Firefox location bar, enter the preference "middlemouse.contentLoadURL" in the filter, and verify the setting appears as 'false' in the 'value' column. If it is set to 'true', double-click anywhere along the row and it will revert to 'false'. Middle-clicking on a tab to close it will now work.
Double Clicking empty space on the Tab Bar will open a 'New Tab.
Double Clicking on a Tab to close a Tab is an option in Tab Clicking Options extension.
Double Clicking in the Location Bar selects its entire contents. You can set the user preference "browser.urlbar.doubleClickSelectsAll" to false so that double-click selects a "word" in its contents, and then if the user preference "layout.word_select.stop_at_punctuation" is true (the default in Firefox), double-click will select part of a URL shown in the Location Bar. Triple Clicking always selects the entire contents of the Location Bar.
Double Clicking a file entry in the Downloads Manager will open/launch the file (provided that you haven't moved it from its saved location).
Customize the toolbars
You can adjust your toolbars to your liking. Right click on any toolbar, and select 'Customize'. While this dialogue is up, you can move buttons around on your toolbars by click-and-drag to the new location. The window that pops up when you do this is a holding area for unused icons. You can drag any item from it onto your toolbars to have it made available, and you can drag any icon from your toolbars onto this box to hide that icon completely.
Create a keyword bookmark
Right clicking in a search box (such as the search box on the left of this page) and selecting 'Add a Keyword for this Search' lets you make an interactive keyword bookmark.
View selection source
Right-click on a highlighted area of a page (obtained by click-and-dragging the mouse, for example) and choose 'View selection source' to display the source code for the selected part of the page only.
Drag and Drop
Moving bookmarks and folders
To change a bookmark's position within the same folder by dragging it to your desired position.
To Move a folder to another position or location by dragging the folder to new location.
To move a single bookmark or a selection of bookmarks to another location hold down SHIFT while dragging it to the new location. If you drag a single bookmark, or a selection of bookmarks to a new location without holding down the Shift key, you will copy the bookmark(s). (see Sorting_and_rearranging_bookmarks_-_Firefox)
You can bookmark the current page by dragging the icon from the location bar (or the tab) to your Bookmarks folder. You can also drag it to the desktop to make an icon for that page. Drag a text file, a link, a picture, etcetera... from your folders or your desktop to Firefox and it will open in Firefox!
"Click-and-drag" a bookmark to the main content window (which is the biggest on the Firefox user interface),so you can open it in a new tab! Dragging a link onto a new tab will open the link in the new tab.
Drag any link to the Download Manager Window to add and download the link. You can also directly download anything from a page by drag and dropping it onto the "Downloads" icon in your toolbar (provided you put it there through Customize).