Has deactivating an add-on the same effect as removing?
When I deactivate an add-on, it won't collect any data or something, does it? So it's the same effect than if I removed it?
Wšě wotmołwy (3)
No, not necessarily the same. It depends upon the add-on and what that add-on does.
Is it an extension?
When an extension is disabled, its own code should not run. However, Firefox probably will check for updates, which may involve contacting URLs controlled by the extension's author.
If you want to turn off update checking for an extension, click the "More" link for it on the Add-ons page and you can set that option there.
When you deactivate an addon, then generally it will not work it will be inactive, but you have options to use it again or update it.
If you remove an addon it is no longer on your computer. (Sometimes it may retain some data on the computer). If you wish to use it again you need to re install it.