It's annoying, but not deceitful.
a) What if it was two confirmation popups before you had to leave the page?
b) Three confirmation popups?
c) What if it let you navigate away for about 10 seconds, but then immediately reloaded the last Luxottica page you were on. It only does this once.
d) What if it let you navigate away for about 10 seconds, but then immediately reloaded the last Luxottica page you were on. It does this 2-3 times before it stops redirecting you back and lets you browse freely again.
e) What if it required you to complete a short 5-30 second interactive engagement advertisement-game activity popup before you could leave instead of just clicking "OK I really want to leave".
f) What if it never let you leave unless you quit the browser but you could open other tabs.
g) What if it controlled your browser in such a way that you couldn't quit the browser, and it maximized the window. You can still put other windows on top of it but when you close them, the luxottica store is behind everything until you shut down the whole computer.
h) What if it loaded that page which you can't close every time you started the browser. Only reinstalling the browser makes this stop, until you visit the Luxottica website again and it reloads this functionality again.
i) What if it automatically loaded this page as your desktop background and required downloading a special tool from GitHub to get rid of it.
j) What if it automatically rebranded your entire computer to display Gucci logos throughout the UI. Reinstalling the operating system is the only way to fix it.
Your question is about what's acceptable. My answer is:
1. If the site tricks me (makes me take an action that I would not have taken if the site had not misled me), that's unacceptable. So, roughly any degree of deceit is unacceptable to me.
2. If the site stops me from switching/closing tabs, or changes system settings (like the ones you describe) without me being cognizant of agreeing, that's unacceptable.
Showing 3 popups within a tab when I'm about to close it: that's annoying and douchy, and probably won't work on me, but I won't hate you for it.
From your list, c-j would definitely make me hate you. a and b might be OK if you're presenting me better offers (e.g. 10% off the first time, then 15%, finally 20% off the third time).
That would be harassment. Not even borderline. How would you react if it were to happen on a physical shop?
If the alert says something untrue or misleading (last day of sale, virus on computer, 1000th visitor) that's deceitful.
Plus, it incentivizes having to threaten to cancel a deal to get anywhere near acceptable terms. Fuck that.
But basically off the page as regards to the specific UX patterns under discussion in this thread.
This one:
"when someone tried to leave the site, bring up a popup to offer them a deal or otherwise encourage them not to leave"
In other words: in the Venn diagram of the two buckets - the measure of overlap is quite small.