I don't know if this will help you.

https://support.mozilla.org/en-US/kb/changes-toolbars-and-window-sizes-are-not-saved You may have corrupt xulstore.json or Localstore.rdf file.

Close Firefox. Open your file browser to this hidden location:

• Mac: *~/Library/Application Support/Firefox/Profiles
• Linux: *~/.mozilla/firefox/Profiles
• Windows: %AppData%\Mozilla\Firefox\Profiles
• *C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles
• Windows XP: C:\Documents and Settings\<user>\Application Data
  \Mozilla\Firefox\Profiles\

Search for the above files. Then rename or delete them. Restart Firefox.

FredMcD said

I don't know if this will help you. https://support.mozilla.org/en-US/kb/changes-toolbars-and-window-sizes-are-not-saved You may have corrupt xulstore.json or Localstore.rdf file. Close Firefox. Open your file browser to this hidden location:

• Mac: *~/Library/Application Support/Firefox/Profiles
• Linux: *~/.mozilla/firefox/Profiles
• Windows: %AppData%\Mozilla\Firefox\Profiles
• *C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles
• Windows XP: C:\Documents and Settings\<user>\Application Data
  \Mozilla\Firefox\Profiles\

Search for the above files. Then rename or delete them. Restart Firefox.

Thanks that partially helped I no longer need to kill the browser and it doesn't crash when I minimize but still I cannot resize the window at my own will and when fully maximized grab it from the top bar to drag it along to other screens

Spoke to soon, after a few minutes longer of usage behavior is the same

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

Safe Mode was worst the window doesn't even load I just get the icon on the task bar, I've also tried uninstalling and reinstall, I got a warning at the first start that if I wanted to completely clean the browser o load the old components from the previous install I did this and the behavior is the same.

I have a virtual machine with other windows 10 same version and I got the same behavior. I'm downloading the latest update for windows 10 maybe that helps but any other pointer with firefox will help.

This is an option;

First, Type about:preferences#advanced<enter> in the address bar. Under Advanced, Select Update.

[v56+] Type about:preferences#general<enter> in the address bar. Select Update.

Select Never Check For Updates.

Also turn off Use a background service to install updates

Install Older Version Of Firefox {web link} Be sure to read everything here.

If you still want to downgrade, look under; I still want to downgrade. Click the Directory of other versions and languages link. Look for the directory of the version that you want. But, remember that old versions may have security issues.

You should also check out Firefox; Extended Support Release {web link} ESR Notes System Requirements

Unfortunately that doesn't solve my problem I cannot downgrade as my job is to test my web application in new browsers for incompatibilities or issues, which I have not done properly as my browser window doesn't even act in a proper way

I finally solved it, it's the Theme, Default theme is the one that causes all the issues I had, I switched into light theme and the browser window acts normally now.

That was very good work. Well done. Please flag your last post as Solved Problem so others will know.