How to Activate Java in Firefox: A Step-by-Step Guide

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Run Java apps and content directly in your web browser

Written by Nicole Levine, MFA

Last Updated: December 6, 2025 Fact Checked

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Older Version of Firefox

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Using Microsoft Edge

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Enabling JavaScript

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Video

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Tips

While Firefox (and most other web browsers) no longer support running Java applets in a browser window, there are some simple workarounds. If you require Firefox, you can install an older version of the app (older than Firefox 52), which still supports the Java plugin. If you don't mind using Edge, you can enable Internet Explorer mode, which allows you to turn on Java for trusted websites. This wikiHow guide will teach you how to enable Java in Firefox and Edge. We'll also show you how to enable JavaScript in Firefox if it's disabled.

Can you enable Java on Firefox?

For security reasons, Firefox and most other web browsers no longer support Java. If you want to run a Java applet in your browser, you can install an older version of Firefox, which supports the Java desktop plugin, or use Edge. If you use Edge, enable Internet Explorer mode in ••• > Settings > Default browser.

Method 1

Method 1 of 3:

Using an Older Version of Firefox

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1
Understand the limitations of this method. Due to security issues, current versions of Firefox do not support Java, nor will future versions. To enable Java content, you'll have to install an old, 32-bit version of Firefox and then manually add the Java plugin. This is possible on Windows computers, but Firefox for Mac defaults to 64-bit, making it impossible to install Java for Firefox on a Mac.^{[1]
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- Though this method will work in a pinch, it's not the greatest workaround for these reasons:
  - Closing and re-opening Firefox may result in Firefox updating, which will render Java unusable.
  - Using an old version of Firefox increases the risk of contracting a virus or malware.
  - You can never update your old version of Firefox, as doing so will remove your Java support.
2
Download and install Java. To do so:^{[2]
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- Go to www.java.com/en/download in a browser.
- Click Download Java for Desktops.
- Once the file is downloaded, open your Downloads folder.
- Double-click the downloaded Java setup file.
- Click Yes when prompted.
- Click Install at the bottom of the Java window.
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Go to ftp.mozilla.org/pub/firefox/releases/51.0b9/ in a browser. This is where you can download the last version of Firefox that supported Java.
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Select the 32-bit download link. You'll need to use the 32-bit version of the installer for this trick to work. Click the firefox-51.0b9.win32.sdk.zip link near the bottom of the list of links on this page.
- You may need to click Save or OK to download the file to your computer.
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Unzip the file. To do this:
- Right-click the ZIP file you just downloaded.
- Select Extract all.
- Click Extract.
Double-click the firefox-51.0b9.win32.sdk folder (not the ZIP one) to open it.
It's the only folder in the window.
Double-click this folder, which is near the top of the window, to do so.
It's near the middle of the page. This will prompt the Firefox 51 app to open.
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Disable automatic updates. Type about:config into the Firefox address bar and press ↵ Enter, then do the following:
- Click I accept the risk! when prompted.
- Click the search bar at the top of the page.
- Type in app.update.auto
- Double-click the app.update.auto result to change its value from "true" to "false".
- Be sure to click Not now or Ask later if ever prompted to update.
The menu is in the upper-right side of the window. "Add-ons" is a puzzle piece-shaped icon in the menu.
It's on the left side of the page.
You'll usually find this option near the bottom of the page.
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Click the "Ask to Activate" drop-down box and select Always Activate. This option is in the drop-down menu. Doing so will activate Java for any website that you visit in this version of Firefox, though you must be careful not to update Firefox at all.
- If you accidentally update Firefox or an update gets pushed through, you can reinstall Firefox 51 by deleting the firefox-51.0b9.win32.sdk folder (not the ZIP version), opening the ZIP folder of the same name and re-extracting it, and then re-opening the Firefox 51 app from within the bin folder.
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Go to a website that has a Java applet and click "Activate Java". If you can activate Java, you'll see an option like this on the Java content you want to load.^{[3]
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- If you see a message that says Java is "unsupported", "disabled", "not installed", or something similar instead of the "Activate Java" link, you cannot run the site in question on Firefox.
- If you can't click Activate Java for some reason, or you don't see the option to do so, click the plugin icon in the address bar (it looks like a Lego piece) and select Allow Now.
- You can also click Allow and Remember to place the site on Firefox's "Allowed" list.

Method 2

Method 2 of 3:

Using Microsoft Edge in Internet Explorer Mode

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1
Install Java if you haven't already. While modern web browsers do not support Java, you can still use the Java plugin to run Java applets in a browser window if you're using Edge in Internet Explorer mode. First, if you haven't installed Java, do so now:
- Go to www.java.com/en/download in a browser.
- Click Download Java for Desktops.
- Once the file is downloaded, open your Downloads folder.
- Double-click the downloaded Java setup file.
- Click Yes when prompted.
- Click Install at the bottom of the Java window.
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Open Microsoft Edge. If you don't have Microsoft Edge installed, you can download it from Microsoft.
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Click the three-dot menu ••• and select Settings. You'll see the menu in the upper-right corner of Edge.
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Click Default browser. It's in the left panel.^{[4]
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Turn on Internet Explorer mode. The option to do this varies by version:^{[5]
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- In most versions, you'll select the drop-down menu next to "Allow sites to be reloaded in Internet Explorer mode (IE mode)" to Allow.
- In some versions, you'll need to set "Allow sites to be reloaded in Internet Explorer" to On.
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Close and reopen Edge, then go to a website with a Java applet. After making this change, you have to close Edge and then reopen it for the changes to take effect. Once you've done this, open the website containing the Java applet you want to run.^{[6]
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Add the website to your "Internet Explorer mode pages" list. To do this, copy the URL that contains the Java applet, click Add a page, and paste the copied URL. Click Add to add the site to your list.^{[7]
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- If you're using an Enterprise version of Microsoft Edge, click the three dots at the top-right and select Reload in Internet Explorer mode instead.
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Refresh the page containing the Java applet. You should now be able to run the Java applet.
- If this doesn't work, you may also need to add the website to your Java control panel security settings. To do this:^{[8]
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  - Open the Java control panel.
  - Click the Security tab.
  - Click Edit site list next to "Exceptions".
  - Add the URL to the page containing the Java applet and save.

Method 3

Method 3 of 3:

Enabling JavaScript in Firefox

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JavaScript is usually enabled by default in Firefox. However, if you have ever disabled it, it's easy to turn it back on. Start by typing about:config into the Firefox address bar and pressing ↵ Enter or ⏎ Return.^{[9]
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It's a blue button in the middle of the page.
Click the search bar, then type in javascript.enabled to search for the matching result.
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Review the JavaScript value. If you see "true" below the "value" heading that's on the right side of the page, JavaScript is currently enabled; this is the default Firefox setting.
- If you see "false" below the "value" heading, proceed.
Double-click javascript.enabled near the top of the page. You should see the status below the "value" heading change to "true".^{[10]
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