With the advent of style pages, copy-n-pasting styled text from source HTML is increasingly unlikely to work with pages from different sources, including your own, and when it does, you're probably using deprecated formatting features. Caveat copyor.

For useful keyboard shortcuts, pay attention to the right-hand side of the menus you pull down.

Mozilla provides some web pages with great tips for using Firefox: click

And there's an add-on called Preferential that lets you control many more options than are exposed by the standard Preferences pane: click