script.js

const focusBy = selector => {
  const input = document.querySelector(selector);
  if (input) {
    input.focus();

    const endCursor = input.value.length
    input.setSelectionRange(endCursor, endCursor)

    return true
  }
}

const main = async () => {
  try {
    const { patterns } = await browser.storage.sync.get('patterns')
    if (!patterns) {
      return
    }

    const currentPattern = patterns.find(pattern => {
      const re = new RegExp(pattern.url);
      return document.location.href.match(re);
    })

    if (currentPattern) {
      const selector = currentPattern.selector;
      if (selector && focusBy(selector)) {
        return
      }
    }

    const defaultSelectors = [
      "input[tabIndex='1']",
      "input[class*='search']",
      "input[id*='search']",
      "input[type='search']",
      "input[type='text']"
    ];

    for (const selector of defaultSelectors) {
      if (focusBy(selector))
        break;
    }
  } catch (error) {
    console.error(error)
  }
}

main()