hi, addons hosted at addons.mozilla.org get vetted by mozilla before they go public, so they should be safe to use.

mozillaa said

Are these two addons safe? Can these addons read my mails or read my password when I am typing?

Yes, they can. Addons you install can do everything firefox can, which means that they can view what you do on websites. However, as philipp mentioned, mozilla reviews all the addons at addons.mozilla.org to make sure they don't do anything harmful. So yes, these are safe to use.

If you search the Mozilla download sites of extensions you will find User Reviews which should reassure you and alert you to any limitations or possible problems.