Is it possible using Selenium only, to import an extension into the Safari/Edge/IE webdriver? So that Safari/Edge/IE boots with the extension imported and enabled for testing?
And if possible... How do i do this in Python
I'm pretty sure none of those browsers have support for this in selenium. Your only option is to set up the browsers with extensions before running the tests. Safari and IE will probably never get support for this as the safari driver is deprecated and IE won't get any more updates as the focus will shift fully to Edge.
Microsoft Edge also does not even support extensions in the stable build yet at all.
Edge might get support in the driver once the feature has been rolled out to the stable release, as the Edge driver is created by Microsoft themselves.
NOTE: The SafariDriver is deprecated. All code has been removed from master, but is still available in the safari branch
Personalize and add new features to Microsoft Edge with extensions. Starting with build 14291 for the Windows 10 Insider Preview, a selection of extensions is now available for Microsoft Edge.