Thanks RaceFPV -- that would bother me as well, but I assure you the add-on does not contain reference to any .ru URLs. You can right-click the "Add to Firefox" button and then "Save Link As..." to save the xpi to your Desktop. Then rename the .xpi to a .zip to open it up and view the source files. I am pasting the contents from each relevant file below for reference:

background.js:

const websites = [
{name: 'nytimes.com', pattern: /nytimes.com(\/?.*)/},
{name: 'wsj.com', pattern: /wsj.com(\/?.*)/},
{name: 'washingtonpost.com', pattern: /washingtonpost.com(\/?.*)/},
{name: 'miamiherald.com', pattern: /miamiherald.com(\/?.*)/},
{name: 'reuters.com', pattern: /reuters.com(\/?.*)/},
{name: 'latimes.com', pattern: /latimes.com(\/?.*)/},
{name: 'ft.com', pattern: /ft.com(\/?.*)/},
{name: 'theatlantic.com', pattern: /theatlantic.com(\/?.*)/},
{name: 'bloomberg.com', pattern: /bloomberg.com(\/?.*)/}
];

chrome.webRequest.onBeforeRequest.addListener((details) => {
// Exclude specific paths for nytimes.com
if (
details.url.includes('nytimes.com/puzzles/*') ||
details.url.includes('nytimes.com/games/*') ||
details.url.includes('nytimes.com/crosswords/*')
) {
return;
}

for (const website of websites) {
if (website.pattern.test(details.url) === true) {
return {
redirectUrl: `https://archive.today/?run=1&url=https://www.${website.name}${website.pattern.exec(details.url)[1]}`
};
}
}
}, {
urls: [
'*://*.nytimes.com/*/*',
'*://*.wsj.com/*/*',
'*://*.washingtonpost.com/*/*',
'*://*.miamiherald.com/*/*',
'*://*.reuters.com/*/*',
'*://*.latimes.com/*/*',
'*://*.ft.com/*/*',
'*://*.theatlantic.com/*/*',
'*://*.bloomberg.com/*/*'
],
types: [
'main_frame',
'sub_frame'
]
}, ['blocking']);


and manifest.js:

{
"name": "Surmount",
"description": "Climb over paywalls.",
"version": "3.0",
"manifest_version": 2,
"browser_specific_settings": {
"gecko_android": {},
"gecko": {
"id": "{9a0be525-4e0d-4954-8b9e-1ef2218d851d}"
}
},
"background": {
"scripts": [
"background.js"
]
},
"icons": {
"256": "surmount.png"
},
"permissions": [
"webRequest",
"webRequestBlocking",
"*://*.nytimes.com/*",
"*://*.wsj.com/*",
"*://*.washingtonpost.com/*",
"*://*.miamiherald.com/*",
"*://*.reuters.com/*",
"*://*.latimes.com/*",
"*://*.theintercept.com/*",
"*://*.ft.com/*",
"*://*.theatlantic.com/*",
"*://*.bloomberg.com/*",
"*://*.theathletic.com/*"
]
}

I recommend you install the NoScript add-on if you do not already use it. If you then visit archive.today (which redirects to archive.ph) you will see that NoScript reveals mail.ru is loaded along with the website (which I do not control nor have any affiliation with).

Thank you -- I've fixed the issue preventing The Atlantic's homepage for you. Please try again with the latest version 2.9.