Prev Page per LuskyNavy

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

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/3, hitting the button will go to http://www.site.com/page/2.
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 previous page from http://www.site.com/page/cam005.jpg will go to http://www.site.com/page/cam002.jpg. Skipping dead url will go no more page than the "hole limit".

This is a one button version of this addon : https://cup.aihedy.com/en-US/firefox/addon/nextprev-page/.

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