Where are you looking?

In Windows, in the traditional menu, it is under Tools|Options|Security|Passwords and there is a button to show passwords. In Linux, it is under Edit|Preferences in place of Tools|Options.

In Windows, in the hamburger menu, it is under Options|Options, which probably translates to Preferences|Preferences in Linux.

(I use Linux at home, but Windows here at work, and it can be hard to remember all the little differences between the two.)

I did find Preferences. There is no Password management button or tab.

Below 'General' 'Display' etc I see: 'Junk' 'Email Scams' 'Anti Virus' 'Passwords'

Those should appear as tabs, but agree that yours do not appear that way. Currently, the 'Junk' must be selected as it is showing the 'Junk' information.

Is it possible to click on 'Passwords' word and change the information displayed ?

We Linux users get a few graphical quirks. One is that checkboxes in menus don't appear. Apparently this is related to the use of out-of-date GTK3 libraries, but no-one seems to know what to do about it. There are several reports on bugzilla relating to these display oddities, but little evidence of any action being taken to resolve them.

In this case, it would seem the OP's colour scheme or theme doesn't have any way to render the tab outlines. The slight vertical variation in text position ("Junk" is slightly higher than the other text) does suggest there are tabs, but no outline. Is this Unity?

I have seen something similar with the message and calendar tabs too, but it does vary with the theme being used. I have also had blank tabs where a text label should appear.

As Toad-Hall suggests, do click on Passwords and see what happens.

The attached shows how it appears in Windows 10, so you can see how my tab labels correspond with your line of text.

Maybe something is not quite ok with the thunderbird installation. Try reinstalling Thunderbird using a fresh download. http://ftp.mozilla.org/pub/thunderbird/releases/52.2.1/ select the correct linux type select the prefered language download the thunderbird-52.2.1.tar.bz2 file.

Eek!

Many distros include Thunderbird as the default email app and incorporate it into their repositories, and updates are done via software manager tools such as apt or yum. For users who use Thunderbird as given, switching to direct downloads from the mozilla site is a somewhat tricky operation. I recall Mint and Ubuntu having complicated launcher shell scripts, and moving away from what was provided was rather painful.

There is no trivial way to overwrite the installed Thunderbird with a tarball version. :-(