WTH, Firefox will not uninstall just disable

Check your permissions for Firefox and also set your default browser.
Do this in your phone settings, not Firefox... Then try to uninstall

 

I've never owned a phone (or, more precisely, used a launcher) with an "uninstall icon", so can't say anything about that. And I don't use the Play Store to uninstall anything. My method is to open Settings > Apps, find the app, clear its data (just to be sure), then select uninstall.

The usual reason a user-installed app can't be uninstalled is because it has been made a device administrator, but that shouldn't be the case for Firefox. But maybe check for device admin apps and, if it's there, untick the box then try uninstalling again.

 

What @Hadron said.

Also, I would like to add that if you are trying to save space, Brave is probably not going to help very much.

One of the issues with this is that Brave, FireFox, and other browsers like them have their own Webview as part of the app.
Unfortunately, this adds considerably to the size of the app.

One great way around this is to use a browser that is simply a wrapper for the Android System Webview app that is already installed on every Android device.

Another benefit to doing this is speed.
Your online experience will be greatly accelerated.

Most likely the best browser for the job is Lightning Browser.
It is so good, in fact, that there are various copycat versions of this app floating around.

Currently I use a version that has been included in a downloader app, called IDM+.

The majority of these are legit, by the way, because Lightning- unlike Brave and Firefox- is a FOSS app.

Excellent security, blazing speed, small in size, unlimited tabs and unlimited bookmarks- all in a simple, intuitive browser.

I have nothing to gain from it, I just believe that it really is that good.

https://f-droid.org/en/packages/acr.browser.lightning/

Some legit variants:

https://f-droid.org/en/packages/org.midorinext.android/

https://f-droid.org/en/packages/com.cookiegames.smartcookie/

https://m.apkpure.com/1dm-fastest-video-torrent-downloader-browser/idm.internet.download.manager

 

Dragging the icon on your screen isn't going to uninstall the app, all that does is remove the icon from that screen. The app itself is till installed. As @Dannydet commented on, you need to go into the Settings >> Apps menu, find the Firefox app listing and open it, then tap on the Uninstall button. A more thorough removal is to use Clear data first, then tap on the Uninstall button. Using Clear data will remove all the app's settings and config files, and the app's cache.