https://support.mozilla.org/en-US/kb/keyboard-shortcuts-perform-firefox-tasks-quickly

Ohh.. I'm sorry for not telling that I'm using "Mobile" Mozilla Firefox.

Anyway thanks for your quick reply.

Hi Christ, would you know how can I edit my question?

Thanks! :)

Click the EDIT THIS POST button.

Using mobile view is limited in options. I had to change desktop mode to see the edit button.. again thanks Chris for helping.

Now back to my problem, if anyone there can help me please.. Thanks in advance!

I don't think there's a built-in feature for changing tabs, other than using the tabs list. Maybe an add-on?

The Quick Gestures extension has pre-defined (but changeable) gestures for previous tab and next tab. I used this for a while, but found myself accidentally doing unexpected things (sloppy fingers?) so I no longer use it.

https://addons.mozilla.org/android/addon/quick-gestures/

Ok I'll try that and post an update later.

Thanks jscher2000!

the add-on is cool! This fix my problem! But there is a problem with the certificate of the add-on "This add-on could not be verified by Firefox"

What is the risk using this? Can this access internal memory of the phone? Or save password whenever I log-in to any sites without my consent? Any advice?

Thanks!

Hmm, usually if you install through the menu to the Add-ons site, everything is verified automatically. Meaning that the Add-ons team has digitally signed it. I don't know why yours isn't showing that, but hopefully an update to the add-on will fix it.

Ok, thanks again jscher2000.. the add-on solved my problem.. Keep it up helping other users!

At Christ1 thanks for helping too!