Firefox not in Ubuntu Software Repository

What is the output of:

lsb_release -a; uname -a; apt-cache policy firefox

Thanks

No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 17.04
Release: 17.04
Codename: zesty
Linux marius-ubuntu 4.10.0-35-generic #39-Ubuntu SMP Wed Sep 13 07:45:58 UTC 2017 i686 i686 i686 GNU/Linux

firefox:
  Geïnstalleer: (geen)
  Kandidaat: 56.0+build6-0ubuntu0.17.04.2
  Weergawe tabel:
     56.0+build6-0ubuntu0.17.04.2 500
        500 http://archive.ubuntu.com/ubuntu zesty-updates/main i386 Packages
        500 http://archive.ubuntu.com/ubuntu zesty-security/main i386 Packages
        100 /var/lib/dpkg/status
     50.1.0+build2-0ubuntu1 500
        500 http://archive.ubuntu.com/ubuntu zesty/main i386 Packages

What's so new in the latest version of Firefox that you need?

Also, version 56 was released 8 days ago.... How much more newer do you want?

https://en.wikipedia.org/wiki/Firefox

Firefox is available in the Ubuntu-software application - at least on my system.

I can search for it in the search bar, and I also find it in "Commnication & News - Web Browsers".

The Firefox version installed was 53 or 54 something, and the Software Updater did not have the latest one yet. I had trouble, still have, with Flash Player videos that struggle to stream. On my work's Windows laptop, they stream fine, but not on my Linux Firefox. I was hoping maybe the latest Firefox has something built-in or better Flashplayer support.

If I search for Firefox on my Ubuntu Software, the only results I get is:
Search Firefox Bookmarks Provider
Iceweasel

It also do not show in my "Commnication & News - Web Browsers".

Chrome has built in PepperFlash, not Firefox. Is it OK in Chrome?

Maybe it helps if you reset the local storage of the ubuntu-software application.

Open a terminal and issue the following commands:

gnome-software --quit
rm -rf ~/.cache/software-center
rm -rf ~/.config/software-center

and then start ubuntu-software again (the cache will have to be rebuilt, so the first start will take considerably longer).

Oops, my commands were not correct, you should use these ones:

gnome-software --quit
rm -rf ~/.local/share/gnome-software

and then start Ubuntu-software again.

I tried the commands, but Firefox still do not appear in the Ubuntu Software.

I recommend that you then install it with the command

sudo apt-get install firefox

Thanks. Firefox is now back on my PC.
However, the Ubuntu Software still do not show it.

As a last recommendation: reinstall the Ubuntu Software application:

gnome-software --quit
killall gnome-software
rm -rf ~/.local/share/gnome-software
sudo apt-get install --reinstall gnome-software

and try again.
If this still does not list Firefox on your Ubuntu Software app, then I have run out of ideas. As already told, it is shown on my system.