Hi Liokardo, what kind of mouse or trackball is that? Does it let you set up the side buttons to send Page Up and Page Down to Firefox?

The reason I ask that I'm only aware of Firefox having built-in preference settings for the "middle" mouse button (or scroll wheel). I don't think it has preferences for additional buttons and instead receives some kind of key emulation for those buttons.

The System Details list shows you run an older Firefox 63 version that is no longer supported with security updates.

Please update to the current Firefox 64.0 release.

• Help -> About Firefox
• https://support.mozilla.org/en-US/kb/update-firefox-latest-version

Note that on Linux it will be possible in Firefox 65 to scroll tabs with the mouse scroll wheel as long as the scroll buttons aren't present. If you open that many tabs that the tab scroll buttons appear then you scroll the Tab bar in the usual way.