How to disable drag&drop of links by default?

If you are trying to select text from within a hyperlink on a page and Firefox is trying to drag the link instead, you can override this by holding down the Alt key before beginning your selection.

Unfortunately I don't think there is a way to permanently prevent it from dragging the links (the Alt key temporarily disables clicking links, which you obviously wouldn't want to be permanent).

Note: This is for the Windows version of Firefox. For Linux, you have to hold Alt + Win before selecting. I'm not sure what you would do for Mac.

To prevent that a click into the address bar select the whole string automatically, enter about:config into the firefox location bar and search for the preference named browser.urlbar.clickSelectsAll. Double-click and change that entry to false.