Etymology of "favourite" as a verb

IMO, the verb form of favorite would have slowly started becoming popular at around the same time that Microsoft Internet Explorer did. The Wikipedia page for bookmark states:

Bookmarks are called favorites or Internet shortcuts in Internet Explorer, and by virtue of that browser's large market share, these terms have been synonymous with bookmark since the first browser war.

The first browser war took place between 1995 and the early 2000s.

Internet Explorer 1 was a reworked version of Mosaic and was released in 1995. Among its many customisations, the Bookmarks menu was renamed to Favorites.