That's cool about the WikiSource parallel text+image page view, TIL. Thanks!
As an example flow (since it took a minute to figure out): we can start at https://en.wikisource.org/wiki/1911_Encyclopædia_Britannica then click to navigate/browse volume > section > topic to get to a text page, then click Source tab, then click a Page Number (maybe hunt around for the correct page number), and see the parallel view, text + image. With previous and next page buttons available, retaining the parallel text + image view.
5. Notice the left margin contains hyperlinks like [105] whwere 105 is the page number nd links directl;y to the side-by side view of page 105. Click the [105] link on the left (for example), to get to https://en.wikisource.org/wiki/Page%3AEB1911_-_Volume_02.djv... which shows the text-and-image side by side (for that page).
This flow avoids the hunting-for-the-right page step, by using the direct links.
As an example flow (since it took a minute to figure out): we can start at https://en.wikisource.org/wiki/1911_Encyclopædia_Britannica then click to navigate/browse volume > section > topic to get to a text page, then click Source tab, then click a Page Number (maybe hunt around for the correct page number), and see the parallel view, text + image. With previous and next page buttons available, retaining the parallel text + image view.