To directly address your problem of trying to scrape FB posts in the developer console I wrote a functioning synchronous script that saves all posts to an array and their innerText to another array as it scrolls down through someone's timeline. It will also log a running tally of how many posts have been scraped and then output the array of all collected text upon completion.

NOTES:

• You can choose how long you want the script to pause before scrolling down again. I chose two seconds because some posts were taking a while to load
• My script stops collecting posts once it detects the Facebook generated event "Born on..." since that is the first item on the timeline. You can choose any other criteria you see fit to detect the end of the page. I just found this one to be easiest
• It's more robust to not use CSS selectors since the class names and ids change every time a new instance of Facebook is loaded. A concise alternative is to use xpath instead, which you'll see below.
• You can have multiple browser windows open, but this script will only work if its the active tab of its respective browser window.

console.clear();
const allText = [];
const allPosts = [];
(function scrollAndScrape() {
    console.log('Total posts scraped:', allPosts.length)
    if ($x('//span[contains(text(), "Born on")]').length > 0) {
        console.log('Webscrape complete', '\n', allText)
    } else {
        let visiblePosts = $x('//div[@data-pagelet="ProfileTimeline"]/div')
        for (let i = 0; i < visiblePosts.length; i++) {
            if (!allPosts.includes(visiblePosts[i])) {
                allPosts.push(visiblePosts[i])
                allText.push(visiblePosts[i].innerText)
            }
            window.scrollByLines(100)
        }
        setTimeout(scrollAndScrape, 2000);
    }
})()

The output looks something like this:

...
Total posts scraped: 176
Total posts scraped: 180
Total posts scraped: 187
Total posts scraped: 194
Total posts scraped: 200
Webscrape complete
> Array(200) [TEXT BLOB, TEXT BLOB...]

The text blobs will include lots of special string characters such as new line characters (\n) but once you run your second code snippet (see code block below) the text will print nicely in the console. Additionally, you can always format the postText as you wish using regex.

allText.forEach((postText, index)=>{console.log(index, postText)})

To address the more general issue of Facebook being difficult to scrape I would recommend using Selenium. Its compatible with Java, JavaScript, Python, and Ruby. Selenium is an automated browser tool that supports multiple drivers (firefox, chrome, etc.) and can run with or without a GUI. Selenium is well-documented with a large following so it is easy to find guides, tutorials, etc. Everything my JS snippet above does can be replicated with Selenium. You can follow the same logic:

1. Collect all visible posts in an array
2. Scroll down (an easy way to do this is by using the sendKeys method to trigger the Page Down key event)
3. Collect any new visible posts and save them to the array