Hi, thank you for sharing your Firefox configuration. You have an extension named "Tab Center" that may be responsible. Do you want to try disabling it?

You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions. Then cast a critical eye over the list on the right side. Any extensions that Firefox installs on its own are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything you don't want or don't recognize? If in doubt, disable.

Sometimes a link will appear above a disabled extension to restart Firefox before the change takes effect. You can complete your work on the tab and click one of the links as the last step.

Any improvement?

That worked! Thank you so much, you're a life saver! ^^

Note that you have both Adblock Plus and uBlock Origin installed. It is best to use only one such content blocking extension and uBlock Origin is a good choice. We have seen performance issues with Adblock Plus.