JavaScript JIT compilation can be disabled without turning off JavaScript, but the documented controls are mainly browser-management policies, not ordinary settings. Chrome provides enterprise policy controls, and Firefox documents a site-specific administrator policy. If your goal is only to see how a page behaves without scripts, Chrome DevTools can temporarily disable JavaScript in the current tab—but that is a different setting.
JavaScript off and JIT off are different controls
JavaScript is the language web pages use for interactive behavior. A browser’s just-in-time (JIT) compiler translates JavaScript into machine code while it runs. Disabling JavaScript prevents scripts from running; disabling JIT changes how the browser executes JavaScript while leaving script execution available through other engine paths.
That distinction matters when choosing a control: a JavaScript-off command is useful for testing a page without scripts, but it does not disable JIT alone. The official browser documentation covered here provides JIT-specific controls through managed policies, rather than a universal end-user toggle.
Choose the control that matches your goal
| Option | What it changes | Scope and who can use it |
|---|---|---|
| Chrome DevTools: Disable JavaScript | Stops JavaScript from running; does not selectively disable JIT. | One inspected tab; useful for a temporary page test. |
| Chrome enterprise JIT policy | Controls whether sites may run JavaScript with JIT enabled. | Managed Chrome browsers; can be configured by default and with site-specific rules. |
| Firefox SitePolicies with DisableJit | Disables JIT for matched sites while JavaScript remains enabled. | Administrator policy for matched sites; not a standard user-facing toggle. |
| Firefox JavaScript setting or script-blocking add-on | Turns off or selectively blocks script execution, rather than disabling JIT alone. | User-level script control; not equivalent to a JIT policy. |
Chrome: temporarily turn off JavaScript for one tab
Use this when testing whether a page depends on JavaScript. Google’s DevTools guidance describes a temporary tab-level JavaScript control; it does not provide a JIT-only setting.
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- Open the page and open Chrome DevTools.
- Open the Command Menu with Control+Shift+P on Windows or Linux, or Command+Shift+P on macOS.
- Type javascript, select Disable JavaScript, and press Enter.
- Reload the page to observe its behavior without scripts. Keep DevTools open while the disabled state is in effect.
To restore scripts, use the Command Menu to select Enable JavaScript, or close DevTools. See Chrome DevTools: Disable JavaScript for the documented workflow.
Chrome: disable JIT through enterprise policy
Google’s Chrome Enterprise and Education guidance describes the default choice Allow sites to run JavaScript JIT and the alternative Do not allow sites to run JavaScript JIT. Administrators can also configure URL-specific allow or block controls. Google lists this policy support for Chrome on Windows, Mac, Linux, ChromeOS, and Android. The exact deployment path depends on how the organization manages Chrome; consult Google’s JavaScript JIT policy guidance for the applicable management method.
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The policy reference names JavaScriptJitBlockedForSites, supported from Chrome 93 on desktop, ChromeOS, and Android. Policy matching can be frame-by-frame, and site-level/eTLD+1 matching affects which pages a rule covers. A rule written for a subdomain may not have the effect an administrator expects. Check the current Chrome policy reference and its URL-pattern rules for the deployed browser version before applying a rule.
Google warns that disabling JIT may make web content slower, disable parts of JavaScript including WebAssembly, or cause content to render differently. Its documentation describes the security rationale as rendering content in a more secure way, but does not provide a quantified security benefit or performance figure.
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Firefox: use the administrator SitePolicies policy
Mozilla documents a site-specific JIT control under SitePolicies. For a matched site, the policy can set DisableJit: true. Mozilla’s administrator reference lists compatibility with Firefox 150, Firefox ESR 153, and Firefox Enterprise 150; verify that the installed browser version and policy format match the deployment before rollout. The policy is configured by an administrator, not through an ordinary browser preference. See Mozilla’s SitePolicies reference.
Mozilla cautions that sites may become slow or break when JIT is disabled, and WebAssembly will not execute under this policy. This can be consequential for sites and applications that rely on WebAssembly.
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Why Firefox script controls are not JIT controls
Firefox Help describes JavaScript enablement settings and add-ons such as NoScript, which can allow or block scripts by site. These tools affect whether scripts execute; they do not provide the documented JIT-only behavior of SitePolicies. Mozilla also warns that changing settings in about:config can seriously affect browser stability, security, and performance. Avoid treating javascript.enabled=false as a JIT-off switch. For script blocking, see Mozilla’s JavaScript settings help.
What to expect after disabling JIT
- Pages may run more slowly: both Google and Mozilla warn about performance effects; neither source gives a general slowdown percentage.
- Some site features may fail: vendor documentation warns that pages or parts of JavaScript can break or stop working.
- WebAssembly may be unavailable: Google notes it may be disabled, and Mozilla specifically says it will not execute under Firefox’s site policy.
- Test the sites you actually need: site-specific rules can limit the impact compared with a default policy, but ensure the rules match the intended sites and frames.
Browser policy names, supported versions, and management options can change. The Chrome policy reference was based on Chrome 153.0.8010.52, and Mozilla’s SitePolicies page was last updated October 1, 2026; confirm current documentation and your installed versions when deploying policy.
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