I *added* "pinterest" in a Google search:
https://www.google.com/search?q=tulips%20pinterest
The 1st hit went to:
https://www.pinterest.com/explore/tulip/
Got several large thumbnail pics. Clicked on the top left one (single
purplish open bulb) that was a link to:
https://i.pinimg.com/236x/05/d9/cd/05d9cdb4a4be873427b638610ca68292--purple-tulips-art-gallery.jpg
When I got to that page, I got the constantly spinning 4-dot circle. I
had to permit off-domain scripts from pinterest's content domain
(
pinimg.com). I then got the web page showing the full-size photo.
Clicking on the image opens a pinterest photo page. If I click on that
new image page, I'm taken in a new tab to the source page at deviantart.
If instead I copy the above URL in a new blank tab then I get a blank
page with just the image; i.e., the scripts don't run and I just get the
photo of the tulip.
I revisited
https://www.pinterest.com/explore/tulip/ several times.
Only once did I get their login dialog after clicking on a couple dozen
of different tulip photos on that page. When I hit the login dialog the
first time, I simply unloaded that tab and clicked on the search result
again. Thereafter I did not get a login prompt. I actually wanted to
get a login prompt to see if hitting Esc would make the login dialog
disappear or using some other method that left that tab open on that web
page. Instead of revisiting the same page to retest, I kept clicking on
"More like this" photos on the right side of the page. After a couple
dozen tries, I could not get the login dialog to reappear.
So I copied the URL from the Google search and exited the web browser,
used CCleaner to flush any locally cached data (in case the option in
Firefox to purge all local data on its exit had failed to be complete),
loading Firefox anew, used the Google search URL, clicked on the same
1st hit, got to Pinterest's same page (and had to allow the off-domain
pinimg.com scripts), and still no login prompt. After clicking on
several photos, eventually I got the login prompt.
At the bottom of that prompt dialog is "Not now". So I clicked that.
After a dozen more clicks on different photos, the login prompt never
reappeared. So it looks like they shove the login prompt once per
session but you have a very easy way to get rid of it: just click on the
"Not now" link at the bottom of their dialog.
Every web session has an ID associated with it. You could open in
incognito/private mode to get a different session ID in each window. If
you unload and reload the web browser to revisit a page, you get a new
session ID. So this is probably how they determine if you've already
been presented with their login prompt (which is really easy to bypass
and seems to stick per web session). If you're doing a search on tulips
and repeatedly visiting several hits in the results, you're leaving the
web browser loaded so other hits that go to Pinterest won't show the
login prompt - until you revisit in a new session of the web browser.