There are two screenshot in different site's input box

If text becomes visible when selected, it sounds like a problem of white text on a white background. However, I don't know what causes that.

As a first step toward discovering the cause, could you try setting Firefox to strictly follow page colors and see whether that makes any difference. Let us know what happens:

On the Preferences page:

• Linux: "3-bar" menu button (or Edit menu) > Preferences
• Windows: "3-bar" menu button (or Tools menu) > Options
• Mac: "3-bar" menu button (or Firefox 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 color and Firefox should filter the page down so you can easily find the "Colors" button. Go ahead and click that.

Try changing this setting:

"Override the colors specified by the page with your selections above"

Below that, it usually says

"Only with High Contrast themes"

Click that and change the setting to

"Never"

then click OK to finish the change.

Does that help at all?

Here's a screenshot of that part of the Colors dialog:

Are you possibly using a dark theme in your Linux distribution?

Thank u guys, the problem is I am using some dark theme on my linux distribution, and I solved it if I change back to default or light theme