hello, could you go to the firefox menu ≡ > help ? > troubleshooting information, copy the contents of that page and paste them here into a reply on the forum? this might give us a clue what is going on...

Give Firefox a tune up Try Safe Mode Troubleshooting Information This page contains technical information that might be useful when you're trying to solve a problem. If you are looking for answers to common questions about Firefox, check out our support website. Application Basics Name Firefox Version 39.0 Build ID 20150630154324 Update History Update Channel release User Agent Mozilla/5.0 (Windows NT 5.1; rv:39.0) Gecko/20100101 Firefox/39.0 Profile Folder Enabled Plugins about:plugins Build Configuration about:buildconfig Memory Use about:memory Multiprocess Windows 0/1 (default: false) Crash Reports for the Last 3 Days Report ID Submitted

All Crash Reports Extensions Name Version Enabled ID Avast Online Security 10.2.0.187 false wrc@avast.com Microsoft .NET Framework Assistant 0.0.0 false {20a82645-c095-46ed-80e3-08825760534b} Graphics Adapter Description VIA/S3G UniChrome IGP Adapter Drivers vtdisp Adapter RAM Unknown Asynchronous Pan/Zoom none Device ID 0x7205 Direct2D Enabled Blocked for your graphics card because of unresolved driver issues. DirectWrite Enabled false (0.0.0.0) Driver Date 11-29-2004 Driver Version 6.14.10.194 GPU #2 Active false GPU Accelerated Windows 0/1 Basic (OMTC) Blocked for your graphics card because of unresolved driver issues. Subsys ID 00000000 Vendor ID 0x1106 WebGL Renderer Blocked for your graphics card because of unresolved driver issues. windowLayerManagerRemote true AzureCanvasBackend skia AzureContentBackend cairo AzureFallbackCanvasBackend cairo AzureSkiaAccelerated 0 Important Modified Preferences Name Value browser.cache.disk.capacity 358400 browser.cache.disk.filesystem_reported 1 browser.cache.disk.smart_size.first_run false browser.cache.frecency_experiment 1 browser.download.importedFromSqlite true browser.places.smartBookmarksVersion 7 browser.sessionstore.upgradeBackup.latestBuildID 20150630154324 browser.startup.homepage https://login.bayspringstel.net/ browser.startup.homepage_override.buildID 20150630154324 browser.startup.homepage_override.mstone 39.0 dom.mozApps.used true extensions.lastAppVersion 39.0 media.gmp-gmpopenh264.lastUpdate 1438217216 media.gmp-gmpopenh264.version 1.4 media.gmp-manager.buildID 20150630154324 media.gmp-manager.lastCheck 1438457947 network.cookie.prefsMigrated true network.predictor.cleaned-up true places.history.expiration.transient_current_max_pages 18442 plugin.disable_full_page_plugin_for_types application/pdf plugin.importedState true privacy.sanitize.migrateFx3Prefs true storage.vacuum.last.index 0 Important Locked Preferences Name Value JavaScript Incremental GC true Accessibility Activated false Prevent Accessibility 0 Library Versions Expected minimum version Version in use NSPR 4.10.8 4.10.8 NSS 3.19.2 Basic ECC 3.19.2 Basic ECC NSSSMIME 3.19.2 Basic ECC 3.19.2 Basic ECC NSSSSL 3.19.2 Basic ECC 3.19.2 Basic ECC NSSUTIL 3.19.2 3.19.2 Experimental Features Name ID Description Active End Date Homepage

ok, this really looks like an old system - unfortunately i don't know what kind of performance you'd have to expect on such a system, but maybe you can try the following steps and see if they improve the situation:

• disable hardware acceleration in the firefox menu ≡ > options > advanced > general (that setting will take a restart of the browser to take effect) as this cause more troubles on older systems than doing good. in order to disable hardware acceleration in flash please see https://forums.adobe.com/thread/891337
• set plugin content not to be run by default, but only on demand when you really need it: go to the menu ≡ > addons > plugins and set all entries to "ask to activate"
• enable tracking protection in firefox: enter about:config into the firefox address bar (confirm the info message in case it shows up) & search for the preference named privacy.trackingprotection.enabled. double-click it and change its value to true.
• use some addons like bluhell firewall or noscript to ease the load...