Anything beyond two hashtags is excessive. This extension reduces the visibility tweets with more than three hashtags. Best of all, it's completely open source—and less than thirty actual lines of code.
https://github.com/milesmcc/stoptwitterspam

StopTwitterSpam - Reduce Tweet Visibility
StopTwitterSpam is a Firefox add-on that reduces the visibility of tweets with more than three hashtags. It is completely open source and consists of less than thirty lines of code.
Add-on stats
Manifest V2
By: Miles McCain
Daily users: -
Firefox on Android: Yes
Size: 585.70K
Email: st*****@sendmiles.email
URLs: Website
Source: Firefox Browser Add-ons
Add-on safety
Risk impact
StopTwitterSpam requires a few sensitive permissions. Exercise caution before installing.
Risk impact analysis details
- Critical Request access to the following domains: twitter.com
- High ******* ******* **** *** ****** ***** *** ***** ** ******* **** ********* ********* ** * *********** *****
Risk likelihood
StopTwitterSpam is probably trust-worthy. Prefer other publishers if available. Exercise caution when installing this add-on.
Risk likelihood analysis details
- High This extension has low user count. Unpopular extensions may not be stable or safe.
- Low **** ********* *** ******* **** **** * ****** **** ***** ******** *** **** ****** ** ** ****** *** *****
- Low **** ********* *** ***** **** **** * ****** **** ***** ********** *** **** ****** ** ** ****** *** *****
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