Could you start by scanning your system first? This article lists a number of effective cleaners that are free or free trials:

Troubleshoot Firefox issues caused by malware

Next, try this method for installing Firefox:

Clean Reinstall

We use this name, but it's not about removing your settings, it's about making sure the program files are clean (no inconsistent or alien code files). As described below, this process does not disturb your existing settings. It's not essential to uninstall Firefox, but you can if you like, saying No to any request about removing personal data.

It only takes a few minutes.

(A) Download a fresh installer for Firefox to a convenient location. You can choose between:

Regular version for Windows 7-10 https://www.mozilla.org/firefox/all/ Note: only runs Flash, no other legacy plugins "Windows" version is standard 32-bit version; to take advantage of more memory, you could switch to the 64-bit version, see: How to switch from 32-bit to 64-bit Firefox

Extended Support Release for Windows XP-10 https://www.mozilla.org/firefox/organizations/all/ Note: Windows (32-bit) runs legacy plugins that ran in Firefox 51; 64-bit runs Flash and Silverlight. If anyone reading this is thinking of switching to the 64-bit version, see: How to switch from 32-bit to 64-bit Firefox

(B) Exit out of Firefox (if applicable).

(C) Using Windows Explorer/My Computer, rename the program folder as follows:

64-bit Windows users with 32-bit Firefox: Rename

C:\Program Files (x86)\Mozilla Firefox

to

C:\Program Files (x86)\OldFirefox

Other Windows/Firefox combinations: Rename

C:\Program Files\Mozilla Firefox

to

C:\Program Files\OldFirefox

(D) Run the installer you downloaded in step (A). It should automatically connect to your existing settings.

Any improvement?

Assuming that you are talking about 'Radio Stream Butler', you'll have to do a little more than to run malware scans :

Go to the 3-bar menu => Addons => Extensions and look for any unfamiliar or suspicious looking extensions.

When you find any :   remove them.

Also look in : 3-bar menu (or 'Tools') => Options => Advanced => Network tab => Under : 'Offline Web Content and User Data'

Do the same in Windows' Control Panel => Programs.

However : most malware will be 'hiding' somewhere, hence the malware scans.

Further information can be found in the article, that jscher2000 already mentioned :
https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no

Run most or all of the listed malware scanners.
They all work differently   -   what one program doesn't pick up, the other might.

Also see : https://www.im-infected.com/adware/how-to-remove-radio-stream-butler.html