Par For the Course
One day I am using Firefox ESR 60.6. Double-clicking on text while editing in Dokuwiki works as expected. The text is selected.
The next day Firefox is updated to 60.7. Double-clicking freezes Firefox. Completely. Losing all work.
Some infuriated debugging reveals the root cause is the Text Link add-on.
For years this add-on has been a helpful tool. The add-on allows double-clicking on a text string URL that is not hyperlinked and treats that text string as a hyperlink to open the URL in a new tab.
In my breakage I was not double-clicking on a text string URL. I was just selecting text.
Works one day and not the next?
Modern software development — update anything and expect breakage somewhere.