NextPrev Page eftir LuskyNavy

This is a very simple replacement for Simple URL flipper https://cup.aihedy.com/fr/firefox/addon/advanced-sequenced-url-flipper/.

Useful if you want to browse forums, threads, images, pages with a version number or anything with a number.

If you have a page like this http://www.site.com/page/2, hitting +1 will go to http://www.site.com/page/3.
Works also with http://www.site.com/page/cam002.jpg or https://www.foundation.org/en-US/browsername/56.0.1/releasenotes/.

Dead url (holes in numbering) are bypassed. If only http://www.site.com/page/cam002.jpg and http://www.site.com/page/cam005.jpg exist, trying to go next page from http://www.site.com/page/cam002.jpg will go to http://www.site.com/page/cam005.jpg. Skipping dead url will go no more page than the "hole limit".

Page number can be incremented or decremented by 1 or 10 (or the "fast forward/backward" value in options).

Dark mode available in options.

Shortcuts for next (Ctrl+Shift+F) and previous (Ctrl+Shift+V) are supported.
Shortcuts can be changed in extensions shortcuts.

This addon also exist in one button version for next and previous page:
https://cup.aihedy.com/en-US/firefox/addon/next_page/
https://cup.aihedy.com/en-US/firefox/addon/prev-page/.

Required permissions :
- activeTab and tabs : to change current url
- storage : to store the options
- <all_urls> : to test url for bypassing dead ones.