More information, in case it helps.
I deactivated ALL plugins with phpmyadmin.
Changed my theme to Twenty Twelve.
Cleaned my browser cache.
Created a brand new user for the testing.
And I still got those two bugs :
- clicking Text or Tab, nothing happens
- no way to click to embed media, or create hyperlinks
I did this to generate an error log :
- clean the error log
- click in the wordpress admin top horizontal bar to create a new blog post
- typed a a title, typed a few words, selected those words and clicked the "chain" icon to make them an hyperlink
Here's the error log as seen in Firefox > Developer Tools > Error log > errors :
Next comes : searching how to downgrade to the previous wordpress for a while.
EDIT : I also tried deleting the wp-admin and wp-includes folder, and reuploading them afresh from a wordpress-3.5.zip as downloaded from wordpress.org : no difference.
EDIT AGAIN : just when I had finished preparing for a downgrade, with double backups, pre-upload in a subfolder of the 3.4.2 files, I thought I could test as well adding
And you know what ? IT WORKED.
For the life of me, I fail to comprehend.