Depending on the addon or toolbar, it could potentially slow down your browser's performance. For example, if you install a lot of toolbars, they may take up valuable resources that could impact your browser's overall speed.
Additionally, some addons and toolbars are designed to run in the background and can use up CPU and memory resources, which can also slow down your browser. However, not all addons and toolbars will have a negative impact on your browser's performance. Some are actually designed to improve speed and efficiency. So it really depends on the particular addon or toolbar you're using.