Can browser add-ons offering user-defined CSS (to override a site's css) see my passwords and userids?

Question

A website I use often has awful pastel text colors which I find hard to read. The text is not crisp and there's low contrast. I know of a couple of browser add-ins that will let me style the pages as I like, but are they safe? Google Chrome warns that they can "read and change all your data on the websites you visit", but I'm not sure what that means exactly. Can such add-ins see my usernames and passwords when I visit online banking sites etc?

Chrome warning

Answer 1

Short answer : Yes. This is how password managers on your computer record your passwords. Any extension with proper permissions can copy your password whether you're on an SSL site or an unencrypted site. Fortunately, in the case of Google Chrome, it reviews all its extensions before putting it into its app store. So the extensions you use probably do not steal your passwords...But as always, you cannot be 100% sure.

Answer 2

While it would obviously vary between browsers and extensions, in all practicality, no.
Important data is encrypted before being sent to site with SSL, which all reputable banking sites have, and is becoming increasingly popular in general.