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Hi, this feature is called Caret Browsing. You can accidentally turn it on by pressing the F7 function key. F7 will also turn it off.

If F7 doesn't work, you can uncheck a box here:

• Windows: "3-bar" menu button (or Tools menu) > Options
• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• Linux: "3-bar" menu button (or Edit menu) > Preferences
• Any system: type or paste about:preferences into the address bar and press Enter/Return to load it

In the search box at the top of the page, type cursor and Firefox should filter to the "Browsing" section.

Uncheck the box for "Always use the cursor keys to navigate within pages"

Success?

By the way, there should be a confirmation dialog when you press F7 to turn on Caret Browsing that looks like the attached.

If this dialog is disabled, then F7 will turn on Caret Browsing automatically.

Here are some related settings:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.

(2) In the search box above the list, type or paste caret and pause while the list is filtered

To restore the F7 warning dialog:

(3) If the accessibility.warn_on_browsewithcaret preference is bolded and "modified" to false, double-click it to restore the default value of true

To prevent the F7 key from triggering caret browsing:

(4) Double-click the accessibility.browsewithcaret_shortcut.enabled preference to switch the value from true to false

Hi YasinOmidi, another user posted this same problem today, so I thought I would check in on whether you were able to use the above replies to get back to normal, or whether you needed further assistance.