You may be unable to use your keyboard arrows to scroll web pages. Instead of that the page appears as if you can edit it, select text with the keyboard as you do in a text editor.

Recall if you accidentally hit the F7 button. This button activates a special Firefox mode called Caret Browsing, or “Allow text to be selected with the keyboard.” This mode changes the effects of the arrow keys, as well as the [Home] and [End] keys.

Allow text to be selected with the keyboard allows you to move through web content as if you were inside a read-only editor. You can use the keyboard to select web content and copy it to the clipboard.

You can enable this feature by selecting Tools / Options, opening the “General” tab in the “Advanced” panel, and checking the “Allow text to be selected with the keyboard” option, or by pressing F7 at any time.

Caret Browsing is a great feature you can use to avoid selecting text with the mouse.