The problem with these sorts of cases is that it can be very difficult to convince search engines that all of these pages need to exist in the index, because technically they are right about the duplicate content factor. (Around 80% is similar enough, as you've mentioned above.)
What's more, your header and footer also play a role in this; I once had to fix a site where pages (that had to exist for legal reasons) had the same header and footer, but different content (two or three HTML paragraphs each) -- and most or these were seen as duplicate content.
The solution is to find creative ways to add useful and original content until you hit the point where Google or Bing no longer see it as duplicate and put it back in the index. (Software like Moz's suite of tools can help to flag potential issues early.)
Make sure that, for every potential problem page:
- Your URL's are unique and distinct.
- Your H1's are unique.
- Your title and description tags are unique and descriptive.
- Ensure that the canonical tags are present on every page and point to their own unique URL.
- Create original structured data markup for each page and include as JSON-LD files.
- Create original Open Graph data markup for each page as well.
- Most importantly, add content: this can include additional paragraphs of copy for your main page subjects (such as the browser at the top of each page in your example URL's), or distinct lists of helpful links on each page, or unique asides, or even comments. Also consider adding images with unique alt tags.
After you do all of this, resubmit your XML Sitemap, or even just the individual pages you just updated, in Google Search Console to be crawled. If the pages are crawled but you still cannot find them in the index, keep adding more content and resubmitting, until it works and the ratio of duplicate content drops to acceptable levels. It'll take creativity, and trial and error. Good luck!
