In some cases, if your visual editor has disappeared, you can get it back using following steps:
With your browser open on the Write Post screen press:
Ctrl and F5 together (Windows)
This will make the page reload and the buttons will appear.
Go to Users > Your Profile.
There is a box “Use the visual editor when writing”.
Check this box.
If you are using the Adblock extension in Firefox, open it, click Preferences, click Exception Rules and add this as a filter: