Malwarebytes AntiExplot is causing Firefox to slow to a crawl when saving files.
As an example, when i go here - https://www.mozilla.org/en-US/firefox/all/, download the x64 version of Firefox i get the "Save File" dialogue box pop up no problem, however under General Settings in Firefox i have "Always ask me where to save files" ticked so i should then get a file save location dialogue box pop up.
However, if i have Firefox ticked Under Exploit Protection in Malwarebytes Protection tab then Firefox freezes for about 20 - 30 seconds before the dialogue box appears and then using it is very slow.
I've also noticed a general sluggishness to Firefox with the Anti Exploit module enabled for Firefox.
If i turn Firefox off under Under Exploit Protection in Malwarebytes Protection tab then all these problems go away.
I run Windows 10 version 10.0.14393 & Windows Defender on 64bit Firefox, however this also happened on 32bit Firefox and whilst using Bitdefender Free.